I could go on and on and on... But the short answer is it is SO much cheaper to sell the V6 and buy a used 392 than to try and cobble one together.
Keep in mind that it is illegal to do this type of engine swap. If the car was VIN'd for a V6, per the Clean Air Act, any replacement cannot exceed the emissions of that stock mill per Federal guidance. In states with emissions taxes, you pay taxes per the vin, so you'd also be running afoul of state tax codes in many states... not to mention that 9 out of 10 insurance companies will not renew your policy if they find out that a V6 to a V8 engine swap is done. If you just don't tell them and you end up having to file a claim, then they tear up your insurance contract on the spot. Seen it done many times.
And, if you're one of the unlucky ones who gets pinched for having an illegal engine swap, you can wave goodbye to the car from its government funded flatbed as they haul it away (I've also seen this a few times as well).