New cam and heads for original 273?

Yes, 318 heads will work on a 273. I would look for a set that has a casting number that ends with '302'. I say this because they are a great upgrade for 273s, and lots of cars from the early to mid eighties had them. Next for a cam I would look into something very mild, like let's say no bigger than the specs of the lunati voodoo 60401. Do you already have a four barrel intake and carb? What about exhaust?