Big Inch Smallblock
Yeah, I forgot about the intake valve guide. That and the spring seats need welding. The front side of the intake guide is too blunt and there isn’t enough material there to make it the correct shape. If you get it close it tends to fracture the guide boss.
So weld up the front of the intake guides and add about .700 to the spring cups. Raise the roof to where it should be and then weld the floor to get it right.
Im saying that would be close to 400 CFM on a 2.100 valve and maybe you could squeeze a 2.125 valve in there with a 1.500 exhaust.