In an attempt to put things into perspective, your little mouse was putting out about 375 horsepower spinning a B impeller 5100 RPM.
The hydraulic roller you have, with 233-degrees duration @ .050 will put your 454's peak power in the low to mid 6K RPM range. You will need a minimum of 575 horsepower to turn that B impeller 6K and over 700 horsepower to spin it 6400.
In contrast, spinning that B impeller 7200 RPM with the mechanical flat will require 1000 horsepower. The pump will stall the engine long before it reaches peak power.
Depending on how your heads are ported, those ports will stall by .700 lift. Any lift less than that is horsepower left on the table. In other words, how much horsepower an engine makes is directly related to valve lift. Valve timing influences the power at each RPM point. Lobe separation angle (LSA) is simply a number calculated from valve opening and closing points, however I am a fan of tight LSAs. Keith is right, the 108 LSA of the mechanical flat will result in reversion but it is really the 96-degrees of overlap. Reducing the duration with the same lobe profile, while retaining the same LSA, will reduce overlap and potential for reversion. IMHO, a 108 LSA really makes an engine pop hard.
Having a 100ci advantage over the SBC, the 454 will produce more torque at every RPM. Cutting down the impeller to match the pump to the power curve of the engine will soften the launch on the initial hit, meaning the pump will burn out until enough water is being fed to the impeller so that it can pull the engine down and absorb all power being produced. I would definitely recommend an inducer and loader.
Not knowing what your heads flow, but assuming no damage was done in the porting process; I would estimate that you could get into the 550+/- horsepower range, depending on your actual head flow numbers.
My suggestions:
1.) Proceed with the hydraulic roller installed straight up. You will need to run good fuel.
2.) Have the mechanical flat reground with less duration, but try not to sacrifice lift.
3.) Run the mechanical and let the pump stall it wherever it may. I would try pushing the limits with advancing the cam timing to get more RPM. MAKE SURE YOU CHECK YOUR PISTON TO VALVE CLEARANCE!!! The intake valve will be the problem side. The more you advance the cam, the less clearance you will have.
Some final thoughts; I would definitely run a ball valve before the Bassett valve. Octane requirements for the mechanical cam will be much less as the dynamic compression ratio will be low as the piston is damn near half-way up the bore before the intake valve closes. Hydraulic lifters are expensive. If you hate running valves, go with the hydraulic roller.
Good luck,
Joe
