Kenny Bell, one of the hi performance transmission builders from the mid 70's, says that a built up TH 350 is only good for about 900 hp and put his transmissions in many championship cars to prove his point. To say that the TH350 is a weak link is too simplistic. They can be modified to take a terrific amount of punishment. The TH 400 is even stronger.
Bob


55 Cameo 396 TH 400 with overdrive
65 Caliente conv
67 BB Caliente conv
67 Mercury 1 Ton
76 GMC 3/4 ton 454ci
84 Buick Turbo Regal