New guy with some basic Dart questions!

I voted for the 340, cause I have one in my car. I think it's a great engine. Also it's easier to install, and work on. More room. Better handling. All classic cars have issues to be sorted through. A 340/360 will have less than a big block. ( cooling,exhaust, handling, etc) It don't sound like you have a lot of experience with this, so make it easier on yourself and your wallet.