In you want to stick with the stock pistons, you will need a small chamber to keep your compression ratio anywhere near 9.0 to 1 or higher....the 290's or 215's would work, even with the stock valves, they're great flowing heads. Oval ports too, so you can use your current intake. Price will vary, but usually you can find them used for anywhere from 100.00 set up to maybe 300 or so...check ebay, want ad books, even swap meets...but be careful that they aren't cracked. Numbers are cast into them on top and bottom. I only listed the last three numbers in the casting, that's how they are usually referred to. Stock size valves are 2.06 intake and 1.72 exhaust...upgrades are commomly 2.19 or 2.25 intake and 1.88 exhaust.