Really need your head flow numbers, induction (manifold), exhaust size to get a better idea of what would be best for your combo, but generally 500" motors like solid cams in the 260 @ .050 range and ~.570-.600 gross lift with that type of gearing. Having a 4 speed gives you a little more leway because you're not as concerned with idle quality.
But for an off the shelf Hydraulic, the old Lunati 30307 240/250 @.050 .520/.547 lift will
the MP 509. Another strong off the rack Juicer is the MP XE grind 251/257 @.050.
I also agree that Tim (Goolsby) at Bullet (was formerly @ Ultradyne) is one of the most Knowledgable cam guys around.