Bill,
I was thinking of a small sized tubular skeleton that would be a stressed backbone. Then just a lite gauge aluminum or glass tunnel that hugged it. If the drive shaft is above the floor level you will have to put a tunnel in it anyway so why not make it serve two purposes?
Something else to think about for anyone building these types of cars. Having fairly short drive shafts can sometimes cause clearance issues. You might consider a Independent Rear Suspension system. The differential housing is permanently fixed letting you build a very close (as in low) floor tunnel. While I know the the cost can sometimes be a factor there are a number of factory cars using IRS units and plenty of crashed ones in the bone yards. They really aren't that hard to adapt to your use. Plus they do draw people's attention. Just something to think about. We're building one based on the small Winters V8 center case. While they now do offer that case in an IRS configuration it was actually to narrow for our purpose so we designed our own side bells to fit our needs. The unit is at Mark William now getting the stub axles and drive plates machined. Once we get it assembled with the inboard brakes I'll see about posting it for you to see. This will not be an ad to sell them as they are targeted for a specialty car we are building. Just giving you something to think about. I'll be in touch.
George
I'm having a hard time visualizing this skeleton arrangement...But it sounds like it would impede access to the transmission from above. One of the many unusual requirements for this build is that everything possible has to be serviceable from above...and if possible from my wheelchair. The transmission and drive shaft tunnel needs to be removable for servicing.
I would have loved to go with an IRS set up, but that's beyond my budget. What I'm using is a $100 T-bird Turbo Coupe 8.8 Trac-Lok disc brake rear end. The suspension is going to be built out of salvaged out dated racing components. This is definitely a low budget K.I.S.S. project.
It's looking like the drive shaft will end up being around 15"-16" long. It looks like the only clearance issue will be the seats not being as low as I would like....but I can live with it. When I start obsessing over it, I look at these...