Before I forget to mention it you can buy new inner wheel well shells from Inland RV.
Mostly I want to comment on how you might support the body. I replaced my floor and did some relatively minor frame repair with the body in place so I did not lift the body entirely off of the frame. However the technique that I used I think could be adapted to work for what you need. First of all let me remind you that you may not be able to just sit the body back down on the frame after installing the flooring on the frame. Your year of trailer probably has the c-channel on the bottom of the u-channel at the base of the walls. I am sure you can tell if this is the case given how much of the floor you have already taken out. The c-channel part may not be included around the cureved ends of the u-channel though. OK so what I am getting at is that you may need to lower the body back on to the frame and then install the flooring. If so your situation might not be all that different than mine from a lifting point of view. If you refer to the photo that I have included you can get a pretty good idea of what I did as follows:
1.) Cut 2x4's to the right dimension to go from side to side of the body right up to the inside of the outer skin.
2.) Cut shorter 2x4 legs and added 1/4" plywood gussets to the tops of them so that they can be attached to the 2x4 cross pieces. The idea here is that the 2x4 cross members are enough above the floor surface that I can insert a small hydralic jack to lift at any point that I want to.
3.) Cut some 3/4" squares of plywood about 4" x 4" that can be used as shims under the 2x4 legs for places where the plywood floor has been removed.
4.) I attached the 2x4 legs to the cross pieces and then attached the cross pieces to the vertical frame members using screws through the vertical member into the 2x4 cross member. I uses something like 1-1/4" pan head screws about 1/8" in diameter and two per 2x4 end.
5. You will notice that you do not have vertical frame members that go all the way to the floor at each location. The help support the body at all the vertical members I used 5/8" plywood strips about 6"or so wide as lengthwise members sitting on top of the 2x4 cross members. I used self drilling/tapping sheet metal screws to attach them to the vertical frame members.
6.) Since you are going to remove the frame from under the shell I would suggest using some 1x2 strips diagonally from side to side. Attach them to the top of the 2x4 cross members. This will help keep the shell straight.
7.) OK now you are ready to lift. You should be able to place a small hydraulic jack under the middle of a 2x4 cross member near one end and sitting on either the plywood subfloor or a piece of plywood sitting on the frame. I would think that an old fashioned car bumper jack would work just fine too. Also a smaller size hydraulic floor jack would work nicely. By the way one of these works just great for dropping axles.
8.) On my unit I have two access hatches in the back area that are directly opposite each other. Near the front the refrigerator access hatch is nearly directly oposite the entry door. I would consider putting a 4x6 through these openings from side to side on edge with perhaps 2' sticking out on each side. You should be able to attach them to your other framework at least at the plywood strips. You can also add a little extra bracing if needed to attach them solidly enough. You could then jack the body up so that it is above the frame far enough to get the frame out and rest the ends of the 4x6 on whatever you like. Depending on what type of jack you have available you could also jack up the ends of the 4x6 one at a time. I would think you would get a more evenly distributed lift by lifting from in the middle though. If you do not have conveniently located access hatches I suppose that you could lift the body a little higher and put your cross pieces under the edge of the body. Another alternative would be to put your cross pieces from side to side through opposite windows and attach to the framwork below with cable or chain. I believe that I read of one person in the forum here that lifted their body off from above using a chain hoist to overhead beams through the ceiling vent openings so there are a lot ways that could work.
9.) Once the frame is out you could easily enough lower the body down and sit it almost on the ground if you like. If you have it on a paved driveway you might need to hold it down with sand bags or the like. If it is on a dirt area you could even set 4x4 posts into the ground at each corner and attach the 4x6 cross members to them.
In general you would reverse the process to put the frame back in place. The vertical legs and shims allow you to put the plywood back in one sheet at a time with the body sitting in place. Just take out the shims a few at a time as you put the floor sheets back in. I used a racheting luggage strap to help pull the body into correct alingment with the frame as I was putting my flooring back in place. The curved end sheets can be put back in from inside if you lay them on the frame in a diagonal position and turn them into position. Of course you have to do this before you put in the sheet that is next to the end sheet. Also if you keep the body pretty well aligned with the frame (before take it off) you can use it to trace a template for the curve that is missing on your plywood end sheets onto cardboard or thin plywood.
A little note about the weight. My unit is a 73 31' unit. Its factory rated GVW wet is 7200 lbs. Dry it is probably more like 4000 lbs. The two axles together all by themselves weigh in at maybe 4 or 500 lbs. If you think about all the weight of the things that you will not be lifting with the body you can get a general idea of how much it will weigh. I would suprised if you will be lifting more than maybe 1500
to 2000 lbs total. That is really not all that much compared to jacking up a 4000 lb car for example.
I hope all these ramblings are of some help to someone...