I'm sure 590 or 600 HP is very doable from a 360. We'll see, since I've scattered the 408 I may just freshen the old 360 and go back at it. But I'm thinking a 4.86 or 5.13 gear at that weight and that short of a tire. I doubt the converter is holding it back unless it has a lot of slip on the top end. The stall speed is fine IMO. I run a 4200 in my car and it works fine. The 360 makes more torque down low than a shorter stroke 340 would.