[Hotrodrobert]

I don't see any info on those heads but they are probably 74-76cc chambers and with your stroke and pistons that is about 8.4:1 compression ratio.
You can run almost any gas you can find but I like power.
The Vortec heads recommended by Rayfinseats would be a huge improvement. They are cheap to buy but you would need a different intake so that is more money, but that would be about 9.4:1 compression ratio but the superior chamber design would mean you probably could still run 87 and the power increase would be OVER 50!! with BETTER fuel economy!!