Bigger valves in 302 heads?

I don't see any benefit to openning a set of valves in a small port. If the cylinder heads have had port work and flow higher than stock, it would only help if the size of the valve is restricting flow. This can only be proven with a side by side bench test, so it's moot on a situation that has no test work, like in your case.

Valve size vs port size should be relative. The most flow and velocity that you can get throughout the entire port, with the smallest valve at the end is always best, to eliminate shrouding and increase volume.

I have a set of 302 heads and I only did mild cleanup on the castings, in the runners to clean up the runners joined areas and burrs. The ports in the 302 head are shaped specifically to increase velocity. They can be used differently with higher flow applications, but those who port and remove the swirl pattern at the valve window, just before the seat are utilizing the head for higher RPM HP to make up for lack of low RPM velocity.

Basically, unless you are doing some pocket work, guide work, overall porting, etc, it's not worth the effort. Think of it like having a gigantic door in a small hallway. You have to walk sideways to get to the door handle and it doesn't make passing through it any more effective. It actually goes the other way and works against you.

I have a set of accidental heads that have 1.88 1.60 valves that are open chamber 318 port size that I got back from a machine shop after sending them 360 J castings and about the only thing I can do with them is port them and deshroud the tight ends near the intake seats for a forced induction engine that will have the cylinders deshrouded.

That cam will like a little port work on those heads, but bigger valves with no port or deshroud work won't increase anything, but turbulence coming into a .030 over 318 cylinder. In fact, an .030" over helps the current intake valve flow transfer better on the tight side of the intake valve to cylinder wall.

If you port exhaust to 1.60, remember that you should be at 70% intake to exhaust flow, so you'll need to make up the difference in your exhaust system, like going with a symetrical int/exh lobe lift or full exhaust. I think you'd be better off with a 2 1/8- 2 1/4 outlet exhaust per side into a 2.5 full exhaust, your current split ratio cam and a 1.5" exhaust valve.