I think it sounds like a smaller locality boa would be perfect for him! Depends on the floor dimensions of his 60 gallon, but a male Hogg Island or a Cay Caulker would be perfect in that.

I had corns and the past, and while I loved them, I found that even as adults alot of them are still pretty quick movers, whereas a nice boa would get some girth on him but still stay pretty short