The only way to really tell if this'll work will be to wreck a perfectly good clutch (unless you can find one from the scrap yard). Drill out the rivets, reassemble temporarily with small bolts, then see if it'll fit inside the flywheel -- you already know it'll fit inside the pressure plate.

You have this shot of the back of the clutch plate -- do you have any shots of it from the side? How 'bout a pic of the back of the flywheel, with no clutch on it?

I dredged up a link of 3800 flywheels, does yours look like either one of the flywheels shown on the following page? http://www.westcoastfiero.com/engine_hardware_90/90_degree_engine_hardware.html

Quoting that article I linked above: "The hub was shaped exactly as IÆd expected protruding out about 7/8" on the flywheel side and none in back.". That sounds about right, doesn't it? The dimensions would be different with your hub, but if they can assemble with that offset, maybe they'd be willing to simply re-rivet your stack?

In a whole different direction, while searching for flywheel pics, I found this tidbit at
http://floridafieros.org/osg/mod.3800-V6.html
option 1: modify a F-body Flywheel: The F-body flywheel (p.n.#24503285) is 1.110 inch thick. This needs to turned down to .840 inch to match the V6 Getrag flywheel thickness.
That's .270" difference, which gets you that much closer if you are running the skinny flywheel and can swap to the thicker one. Verify that the imbalance stays the same, tho (or can be changed). How thick is your current flywheel, and what is it's diameter? 8 bolts, right, with one key'd off-space to set the balance?

Generally, speaking, you need a goal. Do you want 100% engagement? What % will be 'enough?' What's the overall length of the splines in the hub? If they are 1.5" and you are .5" short, I'm a little uncomfortable, but as nice as it would be to get that whole .5", I'd rest pretty easy with the 80-85% engagement that .25" would get you, from any of the methods discussed above.

Randii