it no longer makes sense to convert to a TT because there are so many relatively cheap TT's out there. Ten years ago, when TT's were $13-15,000 and NA's were $5-6,000 a well planned swap was cost effective and made sense. But today you can find a decent TT well under ten grand; many with some very desirable aftermarket parts. So given the fact that you're already suspecting a bad chassis on the NA, I'd cut my losses there and invest whatever I could get for the NA sale into a Twin Turbo and move forward from that point.