what's the biggest cam I can run with the factory 500efi CMI's without having reversion problems

Biggest isnt the best, there is a science behind cam selection. Best start by telling us about your entire set up, boat, engine build sheet etc.....

im looking at a going a different route with the engine since i lost a cylinder in mine. I want to still be able to run my headers and my switchable exhaust. looking going back to a carb motor but the motor im looking at is running a large solid lifter cam instead of hyd. and needs to run dry exhaust so I want to change the cam out so i can run my exhaust

If your still considering the engine I'm thinking about. Valako has a nice Hydraulic Roller Comp grind that would work good with that engine and heads. Lift and duration.

Yes I am Jason. I'll call Jim this week and talk to him. I just want to be able to use my E-tops and switchable exhaust and not have any reversion

Jim runs a real mild cam on his 780HP 565. 230/236.
He can spec a cam. With those heads the lift is important.
I think the same cam he uses would be great in that engine.
I would run those solid Isky's on his hyd roller like I do. Lash them to 0.006"-0.007" and hold on.
They were sent out to Isky and rebuilt .
He can also order the cam for you.

It was a beautiful weekend out in GH so get at it! It won't last

Cam choice will depend on many other factors. It depends on the cubic inches of the engine and head flow.
A cam that causes reversion in a 454 won't necessarily revert water in a 502.

there is a science behind cam selection.