If you go with the 390, use a C6. The easiest way to get the right engine/tranny match is to buy both at the same time. An ideal source is a recent wreck that killed the body and/or frame but still has an intact engine/tranny. I put a 429/C6 that came from a car owned by a kid who wanted to replace with a 460 (I'm thinki' he also got ticked off the first time he had to replace the alternator belt).