1968 AMC 390 with 1973 heads

Hello Ya'll, I'm new here. Way back in the Olden Days(1990) I rebuilt a '68 390. it had the rectangular exhaust ports, and I wanted to use headers on it. I couldn't find any, so I bought a pair of '73, 360 heads, with individual rocker arm studs, off of a Jeep pickup. Deck height became an issue. So, I measured the angle that the intake would need to be. took the Edelbrock intake to the machine shop and had them shave it to match. Now the bolt holes don't match, so, I redrill the holes. Intake holes match up pretty good, so I went for it. I have no idea what the volume of the new heads is, it wanted to diesel on shutdown with a 650 Holley carb.so I assume its still pretty high compression ratio. Holley had just come out with their ProJection 2bbl fuel injection, So I sold my hunting rifle and bought it, Worked great. By the way, it went into a 1973 CJ-5, T-18 trans, D20 xfer case, Dana 30 front axle and Dana 44 rear axle, both with PowerLoc Limited Slips. The combination was awesome for its day.

    Ok, now for my actual question.....I've seen head gaskets of different thicknesses advertised for sale. What thickness would I need to get the heads back up so that I could buy a new intake to get everything to line up again? Is it actually possible? It has been sitting in the back yard for about ten years, So I'm going to tear it apart and see what gives and have the heads rebuilt. It's in my shop right now on a engine stand waiting for Income Tax Refund to get here. Any help will be greatly appreciated.