What IS the casting number? That will make all the difference. There are SOME "small chamber" 350 heads. The vast majority from the '70s/'80s are "large chamber". Large chamber heads will give a very poor "low compression" ratio. With flat-top pistons, you're looking at around 8:1 with 76 CC chambers on the 327. Also, the vast majority of 350 heads have 1.94" intake valves, the same part number as those found in most 327 heads. Determining WHICH 350 head you have will tell the tale.