What head gasket are you running on 302's with large over bore.
Currently have trouble finding suppliers who will make one for a bore of 4.155 that will seal. Any help out there?

I don't know what your intended use is, but if it is intended for competition only, have you considered making one from sheet copper? You can use a stock gasket as a template and enlarge the bore holes. Of course with today's CNC/water jet/plasma cutter/etc. technology it is easier than ever. Just search the limitations of using copper (O-rings, coolant, etc.).

Thanks for the reply. Currently have a copper gasket from a good co. but can't seem to keep it sealed. Have had the head surfaced and checked, yes it's flat. Checked the deck, yup it's flat. Used copper spray per instructions. It leaks between 1-2-3 only (the hottest part). torqued to 120 fp. Next step is studs, maybe going to 9/16". What next?

Have the deck of the engine machined for "O" rings!

Copper head gaskets should be annealed periodically for best results. BTW, they rarely seal perfectly. That is why I mentioned that they do have limitations. OK for a race application where the coolant can be drained between races, as they sometimes will seep coolant out - however, they are "blowout proof" so that makes them a good choice for a race motor. Yes, O-rings should also be used with about .006" "stick out" above the deck.

Instead of copper spray try red hi-temp silicone sealer lightly smeared around the bore edges only.

One more thing - what is the application? Drag, LSR, circle track?

How much pressure are you using in the cooling system? Consider reducing it if you are drag racing in short bursts of WOT. I use a pressure bleed into a puke tank. For longer runs like LSR or circle track this is not feasible as localized boiling above the combustion chambers over longer periods will be problematic.