whats my Horsepower gain with these mods?

SS did you mention 2 1/4" exhaust as being beneficial to the slant?

Yup yup. But it needs to be in conjunction with a larger carburetor to really see the fullest benefit. Of course headers will help too. I plan on running 2 2.5" into a flowmaster scavenging Y and then out with a 3" single through a Flow Tech Terminator.