If you're going to use an automatic then you will need the complete flywheel adapter housing flexplate from a Turbo 400 GMC pickup built from 66-69 provided you have the six bolt style flange crankshaft. Otherwise you can get a modern adapter setup from Bendtsens that just uses a flexplate and also requires a modern high speed reduction starter motor. Other things to consider are adapting earlier pickup V6 motor mount brackets to the frame and whether you are going to use an electric cooling fan or belt driven fan. If you use the belt driven fan then you will need the light duty pickup truck water pump housing which sits lower, that also requires using the 305,351 and 379 timing chain and sprockets which eliminates the 3 piece gear drive. I did a similar conversion on my 68 using the 478M but it was easier since the truck already was equipped with the 305E
