I ran a turbo 400 with a BBC and I used a shift kit along with a large tranny cooler. I never experienced any issues. I am now building a 30 Model A roadster which will be running a BBC and a turbo 400. It is a professionally built tranny and I will be running an external finned long cooler along with a tranny cooler which is fan activated. Hopefully I will not encounter any overheating issues.