hi mate

if you use a 2wd bottom end or 2wd pistons on a 4wd head you will up the compression by .3

so lays say if the 4wd head on 205 or 200 block and 2wd pistons are standard ( not been skimed or dected in any way,) the compression will be 8:3:1

same way if you use 2wd head/ on 205 or 200 block with 4wd pistons it lowers the comprssion by .3 so it will be 7:7:1

hope this helps

marco