My understanding is that the 200 4R overdrive trans is a 200 with the overdrive stuck on the back, and there are several nationally known 200 4R builders in the turbocharged Buick Grand National world that can build them to handle 800-1000 hp on the dragstrip. None near you, of course
. I'd start with Lonnie Diers at Extreme Automatics in Cincinnati, OH, or Jimmy's Transmissions in Mundelein, IL (by Chicago). Actually, I'd go to www.turbobuick.com
and browse the transmissions forum and post there.