The 200-4R has both the Chevy and BOP bolt pattern, same spline count, and is the same overall length as the ST300. But the trans mounting pad is not in the same position. Good news is, the 200-4R trans mount is in the same position as the short tail TH400. In other words, switch to a TH400 cross-member and it's a bolt in.

You'll need a bracket to hook up the TV cable to the carb linkage, and control kit for the convertor lock-up. (These should be available through B&M and others). And finally, a shifter conversion kit from Shiftworks, so you can control all four gears manually. The 200-4R has a much deeper first gear, so it will improve acceleration (and even city mpg as you won't need as much throttle), while the overdrive improves fuel economy.

Heck even if the V8 doesn't pan out, the improvements in off-line acceleration and fuel economy would still be worth the swap.