Can a 400BBM w/cheap aluminum heads compete/dominate against the street LS?

My LS experience is hauling LS engines from the junkyard for my co-worker.
He has a AMC Spirit, with a completly stock 5.3 except it has a set of headers, aluminum intake and a holley carb, th350 trans, and a early bronco 9" all junkyard parts, but he did rebuild the trans himself and add a 3500 stall converter.
Nothing at all was done to the engine but pressure wash and painted.
12.5 sec in the 1/4 on street drag radials spinning down the track.
It is pretty impressive for how low buck it is.

I stopped over his place yesterday to say hi, and he was mocking up and old trashed chevy truck to play with, He was making the exhaust 5" for the huge turbo he put in the truck.
This engine he actually put some money in, so it is going to be stupid fast.