Libertysyclone
As the old saying goes: I would like to be back at your age and know what I do today. It would be nice to be able to crawl under the rod without having a back ache the next day. My first real Hot Rod, 48 Merc ragtop with a full house flathead, was built in 1958, during my junior year in High School. Got into Chevys when the guys with the power pack 265's started blowing my doors off.
As to your question about small blocks, just about everything will interchange. heads, manifold crank cam, etc. The trick is to match things for fit and purpose. As previously mentioned, the cranks have different journal diameters. Blocks have to match the crank or special bearings can be obtained. Heads will bolt on but you dont want small chamber heads on a block that is decked, or one containing 13 to 1 pistons. You have to pick and choose parts to come up with the correct combination for your application. Finding the interchangability data you need is a big part of the job, and the internet makes it a lot easier the find than it was 20 years ago.
As for the port injection, IMHO you would be hard pressed to beat the GM TPI setup. It works great for the street, and there are people (not me) who can tell you how to tweak it to perform on the track as well. As with all FI setups, it ain't cheap, but HorsePower is directly proportional to $$.