We recently did (3 years ago) an 81 Z28 that was originally a 350 with a TH350 lock up trans. New engine is a GM ZZ 383 rated at 425hp. Bowtie Overdrive provided a 200R4, 2200 stall converter, rear cross member and TV cable. Original drive shaft and yoke worked perfectly. To date no issues. A professionally built 200R4 is fine for a moderate street car in the 450hp, 500tq range. Upside to the 200R4 besides overdrive is it's first three ratios mirror a TH350.