70 Still getting hot, what else to look for?

the main thing that could be tight are the pistons to the clyinder walls and or the ring gap. what is the piston to wall clearance? what is the ring gap? If you used standard rings they are high tension and it will run hot untill they seat in alt least that is what i came up with after tearing my engine apart after around 600 very light miles on it due to overheating and its real close to what your engine is except I rebuilt the bottom end too and I just wanted to check and make sure I didnt mess something up building it. Upon dissasembly I noticed the pistons seemed to have exsessive friction comming from them I checked the crank and it turned really free so I rechecked the piston clearances I have kb hyperneumatic pistons so I set the piston to wall a little tighter cuz they dont expand as much as forged and I set the ring gap to what I thought was the reccomended clearance at .010 and .012 and my machinist said that they may be binding but the cylinder walls wernt scuffed so we decided to set the ring gap alot looser and it acually ended up with more cranking compression and it still ran hot for only about 350 or so miles and it only got hot at idle then it went away I acually switched to a alum rad during this also before tearing it apart and it made it a little better but didnt fix it this is just a thought if you have covered all the regular cooling basics like you mentioned. good luck