lots o fun
if you have a shower pan, then i guess that you have a 3/4 mid or corner bath, not a full rear bath.
I highly recommend you order a service manual for your particular model, as the information i'm about to give you is straight out of it, and is typical of the procedural descriptions, including some illustrations.
this is copyrighted info, so i may be moderated, or shot.
the service manual can be ordered from helen davis of secretarial services. you can find her phone number on this website, by searching for her name.
Shower Pan Removal and Replacement for 1972 Land Yacht:
1. disconnect city water supply
2. shut off water pump switch
3. cover floor with protection material
4. remove access cover for trap located directly below shower pan drain in underbelly. (i assume you already dropped the belly pan, and that was how you determined that you had to take out the shower pan. if that is a bad assumption, let me know).
5. loosen plastic trap union nut and thread trap and plastic adaptor off.
6. with "spanner" type wrench, thread waste fitting out while holding mounting nut below.
7. remove stop screw from upper bath slide door track.
8. drill out stop rivet in plastic lower track
9. slide door past lower track and pull bottom toward you, and unhook slides from upper track.
10. Remove shower curtain.
11. drill out the plastic guide for the bath door
12. remove plastic trim from extrusion just below the toilet pan, using a #30 drill, to drill out the pop rivets and remove the extrusion.
13. remove 2 screws holding lower wardrobe door frame extrusion to shower pan
14. remove toilet assembly and the floor flange.
15. raise toilet pan and block it up far enough to clear the shower pan.
16. cut seaer and remove rivets behind slide door bottom track.
17. remove screws and rivets into wall through pan under lavatory cabinet, above the drain hole.
18. remove 2 screws in wall of storage cabinet under lavatory directly below trap.
19. carefully work shower pan upward from the front edge until it clears lavatory cabinet and remove it standing on edge
20. replace by reversing the above procedure
21. reseal all seams with GE Silicone sealer
22. water test all plumbing and waste lines.
... and that's it... if you have a 3/4 bath similar to the 1972 model.
to replace the floor section under there, hopefully you don't have to rip out the plywood within 12" of the wall. if so, investigate whether a penetrating epoxy could be used in your circumstance, in lieu of actually tearing out the plywood. The job is tripled in complexity of you have to take out plywood from beneath the floor channels.. and replace it.