If the engine is built correctly, reliability should not be a problem. BUT driveability CAN be. As might be fuel costs when gasoline of adequate octane WILL increase in the future. If you desire to mimic the current 500 horsepower street motors, then you'll spend a lot on computerized controls for fuel and such. Check the price of "crate motors" to get an idea of what they're going for, at those power levels, too. Nothing's "cheap" in that orientations.
There's a segment on "Nick's Garage" where he dynos a rebuilt 440/375 and it hits that power level. Getting it to 400+ horsepower might take a few more tweaks, I suspect. Street Hemi 282/284 cam (or similar), some head porting, better intake manifold, a little bigger carb, etc. Plus appropriate-sized exhaust.
Just remember that the more cam, the "more gear in the rear" that you'll need. Plus a little looser torque converters so it'll idle decently at about 750rpm.
With appropriate clutch material upgrades in the automatic trans, or a better clutch mechanism if it's a manual trans.
It's always more fun when you can have fun and nothing breaks! RESPONSIVE power at lower power levels can be more fun than having a total horsepower number to "mention" at car gatherings! A properly set-up chassis can make a lower-powered car outrun a higher powered car, too. Nobody really knows what a '500 horsepower motor" looks like, as most of the things that make that power are hidden internally, anyway. Unless, of course, if it is a 426 HEMI or similar.
CBODY67
