Engine choice selection

[Destructo]

Hey guys and girls, I have been lurking around a bit in search of some ideas and answers.
I am looking to get into my first build and I'd like to go with a mid-sixties Chevelle or a mid-sixties to early 70's Nova for a pro-touring style build. Mostly street, a little track fun sometimes.
Which brings me to my primary question: which engine to go with?
I am thinking an LS3 or LS7, the catch being I want to build the engine myself over time to get the experience then acquire one of the cars. When I have the money for a proper donor.
Thoughts and suggestions on going this route? my primary motivation is to keep costs low and gain the knowledge and experience, should I be worried about trying get one of these motors in either of these cars? I know it'll take some work, but should I be really worried about it? Thanks in advance everyone!