Horse Power Potential of Cylinder Heads

Just my opinion but if money is a potential issue I would not bother with the hydraulic roller setup. If this has to run on pump gas I would also not use the 16cc piston with an open chamber iron head. If your heads can't flow enough you wont make good power in the rpms you're talking about. For some perspective a good set of as-cast factory iron heads that have a modern 5 angle valve job and back cut intake valves might get to 225-230cfm. Add in the smaller cam and you're just not going to do much with them. If you want to go for "max power" then look into a set of RPMs or similar aluminum. If your heads need work, and then need porting, you will be pretty close budget wise to a set of better heads that also give you a closed chamber to work with. You could also go with newer iron stuff but they are heavy and price waise are still pretty similar to aluminum. Do not plan to run any aluminum head out of the box - plan for a valve job on them at least.
If you have heads that will flow in the 240-250 range, and if the static is kept reasopnable for whatever head you go with, then you can expect to make some decent power. 450hp is mild for these. 500+ is easy with porting on better heads and a pretty mild camshaft.