The TH700R4 has a bad reputation from guys who have tried to race it, or run it behind a powerful engine. I do have an 84 Caprice with 240,000 miles on it, the TH700R4 is stock and original and runs just fine... Behind s stock 250, it should live for ever, at least!
My 57 Suburban has a 250ci with a TH350 and the TH700R4 is a direct replacement for a TH350. The driveshaft will need to be shortened and you will need a way to lock the converter, available aftermarket, I do not remember who right now...
Check for clearance and don't forget to mount the TV cable properly!
Pretty easy overall!
