Best rear gears for my combo?

You should settle your mind on what you're doing with the engine.

If it were me, and no cam swap, and just a cruiser, I'd stick with the 7 1/4 with the gears you have.

Now, if you are swapping cams and want a little more pep in your step, forget that. 8 1/4 with 3:23's would be a nice change.

If'n you're gonna beat on it step up to an 8 3/4 with 3:55's (a little more fun factor).