John, I'm one of Oregon Coasts OSR Teammates and saw that you were asking if anyone had any ideas regarding your overheating after the rebuild. I did experience similar situation several decades ago, after rebuilding the top end on my 63 BSA Starfire C15, a small 250 cc single four stroke. It was a little low on power when first reassembled and when I took it out for a ride the exhaust pipe got super hot, almost red. I took it back apart and discovered I had the cam off by a couple teeth. I think it was allowing the exhaust valve to open too soon and thus bleeding off the exhaust gas before the combustion cycle was completed. As soon as the cam timing was corrected it was back to normal. I quickly read through your whole thread, but need to ask, does it have as much power as it did before the rebuild? Is it improved or worse?