Thanks for the download on your frame design ideas and progress. I've looked at alternatives to a Vette/Jag/Ford T-Bird IRS, and while there are a few really custom set-up's there isn't a long track record on most of those custom set-ups. The only truly stock set-up that looks like it would work without changing the hub-to-hub distance is either a Miata or BMW 3-series. Both have a significant selection of aftermarket parts available (shocks, caster/camber kits, brakes, rotors, etc.) and can be upgraded to handle pro-touring engine power and abuse.
Sounds like you and I are in the same boat, the harder I look at the car the more rust/rot/damage I find, which has me leaning away from the Sweedish Ops replacement k-member and 4-link set-up. Besides, the more I think about blowing out the floor and going 100% custom, the more possibilities open up.
Good thing I have another car to finish before I make any commitments.......