Crate Motor

Just my 2 cents, and maybe a few things to think about
Depending on how original the car is, I'd keep the # matching motor for a few reasons
First off you're giving it to your son, and sure A bodies aren't in big demand now, who knows what the future will bring? And every year that goes past, the fewer original old cars there are.
Back when I was 18 I had a chance to buy a 68 road runner for $800, mom wouldn't co-sign for it(sounded too radical) so I got the 69 mach 1 for the same price, I dare you add another zero and find one for twice that today
Station wagons, old cop cars, even 4 doors are getting a following and becoming desirable
Finally, the day may come when your son would like to put it back to bone stock, and it would be nice to have the original motor sitting in a corner
Lets be honest, what is the value of a random 340 short block today vs a # matching motor 20 years from now?