Though I've never owned one, I agree with caferacerx, the 340s were great engines. 500 does seem pretty cheap for it too. If you really want to go with a big block, you could almost buy the 340 and sell it for a bit of profit to help fund the BB.
YES! Sinister beat me to it. Buy both motors if you can afford it. $300 for a rebuilt 383 is a steal too,especially if it runs or can be made to run easy. Heck the pistons in the 383 are worth $300.
