i got a set of 305 heads and i work in a machine shop, i know these engines are kinda low compresion so i was thinkin of milling some material off the heads to raise the compression but still be able to run pump gas and have clearance for the valves? also while i have the heads on the milli was thinkinkin of milling some material out of the intake and exhaust ports and then clean up by polishing them how much materail can i take out of each side without running into problems or would it be better tto just port them regularily