Slant 6 with 200r4?
There's possibly a good reason why there wasn't much demand for the adapter. See what the link below does for you.
http://www.webrodder.com/article.php?AID=426&SID=6
It makes me laugh! My car runs a TH-200-4R, so does my wife's. Hers is a fire-breathing, rip-snorting 1986 Buick Grand National that put 763HP to the rollers and runs mid-10's on wrinkle-wall slicks at 3900lbs. It's a little easier on the trans than mine.
Yes, I said EASIER: mine is a 4600lb 1979 Coupe de Ville with a 542ci stroker Cad engine and 3.08 gears...12.40 on drag radials, 11.97 on nitrous. I have about 75,000 miles on the trans. It was worth a tenth (and 1.5MPG) over the TH-475/2.73 gear combo it replaced.
Note: we both run lockup converters.
The TH700 is OK, but the huge ratio splits (3.06 first gear!) are not good for a drag car.