any engine that makes the blade go around and around is an engine.
output shaft length and output shaft outside diameter are the determining factors, not horsepower output.
is the output shaft keyed? single keyway? two half-moon keys? splined shaft?
bolt pattern on deck mounting flange is easily remedied with sharp 3/8" drill bit and steady hand.
TORO: ******* set-up on the blade, blade driver, and bushing. you'll need to check shaft diameter on the Predator and make sure the Toro drive stuff will fit.
other details:
where does the exhaust exit? toward the operator? directly at a wheel that will get melted? or (worse) directly at the bag?
where does the dead-man switch cable ("zone" cable aka "control" cable) hook up? left side? right side? front?
you can always rotate the clock position of the engine to suit your needs. the lawnmower doesn't care which way the engine is pointed, but you have to make sure everything hooks up correctly.