I've got a TB 4.2 in my 68 Firebird; It's going to get a GT42R turbo. The Wagon you speak of made 1350hp with 21psi, lots of head work, and a GT47 turbo. It also has the bottom-end sleeved with custom pistons.
The TB engine is a bit bigger, but it's waaaaaay ahead of a 7M, much less a 2JZTE. I'll post pics of the stock internals if you like- you'll see it's pretty tough to beat.
Here's mine:
