[JLMounce]

Is e85 readily available in your area? Since it sounds like you already have the speedmaster heads, the way I would run this deal is with E85. Realistically I'd actually want a bit more compression with this fuel type.

Imputing the following information into Wallace Racing's compression calculator I come up with 11.46:1 compression ratio.

4.15 bore
4.25 stroke
72 CC heads
6.6 cc piston valve reliefs
.039" head gasket crush (typical of FelPro 1016 gasket)
4.3" head gasket bore
0.010 deck height.

E85 would be quite safe on this combination. You'd just need to setup the fuel system and carburetor to run it. If the block needs decked and you can get that down to about .005 or even to 0, adding some compression would work. All of this doesn't mean much if you don't have E85 readily available in your area though.

If that's the case, I wouldn't even try to use the speedmaster heads. I'd sell those to fund a KRE or Edelbrock D port head. At 85/87cc's you're below 10.5:1 compression with a standard FelPro 1016 head gasket, unless your pistons have a dome. With a cam in the 230ish range on 112 lsa, it would be pump gas friendly with enough room to forgive poor gas or a tune that isn't spot on. The mid 11:1 ratio from the speedmaster heads should be possible on pump gas, but it's going to take extreme attention to detail in cam selection, tuning and heat management, with little room for error if you get a tank of crap gas. For a street car, you don't want to deal with that I don't think.