Dont waste your time on a LT1, takes alot more to make the same power, more of a PITA to work on, the previously mentioned OPTI is a PITA because the front of the motor needs to come apart to change it.
I used to own GMR SPEED, so some of you know me, I have had many experience with these. If you look hard enough and are willing to travel a little bit you can find some pretty nice LSx cars for under $6k. Even if a car is in Florida, its a $75 plane ticket, and about $150 and a day of your time in gas, so dont be discouraged if the car is far away.
If your son is looking for something to learn on, LSx is the way to go as that is the layout for most performance engines in use by GM today and seems to be for many many years to come.
But that is just my .02...