1974. Not much different from ours, 1973.
The one-piece ceiling is "bonded" to the outer shell with a kind of insulative material, and is molded and engineered to hold the cabinets and walls in place. I wouldn't take it out.
That was why, although we considered a front bed/table, we ended up just putting the closet back, because that "central front" wall really adds support to the ceiling.
We, too, made the back bed into a full-time bed, going back and forth between a "full size" and a modified "twin" with two permanent side seats near the trailer center. That's what we finally decided on. You can see that somewhat in this picuture.
We put extra-sturdy supports under the upper galley cabinet, replaced all the hollow upright walls (side closet and front closet) with 1/2" plywood, screwed into the moded niches designed to hold those walls in place...
We spent 9 months tearing everything out, planning, measuring, sourcing, and redesigning--and discovered the amerigo is really a beautifully-engineered item, each part carefully planned to hold the rest of it together properly. It was like a jib-saw puzzle. The few things we remodeled--well, some we're quite happy with, others, like the tunnel inside the central step-up in the middle of the floor, we'd have left alone if we'd realized how the rest of the inside fit around it and what it was for (allowing the gas lines to run from the port side to the starboard side).
YMMV, of course...you need to find and look at SteveV's amerigo project, his is much like ours and yours, and he's doing some extensive changes.
Anyway, here's ours: