Maybe this would help?
Iím thinking maybe you would be better off cutting the belly pan into 3 pieces. Make one cut just before the axels, and then another cut after the axels. Then you can fairly easily remove the front and rear pieces, and hopefully, flex the remaining piece enough to get it out from the axels.
When they build these puppies, the axels are installed after the floor and belly skin, which explains why things are the way they are now when youíre trying to remove it.
When you reinstall the belly skin, youíll have to seam where you made the cuts. To do that, cut about a 4 or 6 inch wide strip of sheet aluminum and use that, along with pop rivets, to make the seam. If you can make the cut near one of the cross pieces that the belly is riveted to, then the seam reinforcement piece will be supported by additional rivets when you re-install it. Hopefully that makes sense.
The belly skin doesnít need to be completely water tight, or necessarily really pretty, so having the extra seams would not be an issue. Plus, they might come in handy down the road if you need to get access up there again.
Just a thought.