Thanks Mike. All points to the block, which is odd because it's always had good antifreeze and never been abused. I'll pull the oil pan and use some florescent fluid in the cooling system to hopefully pinpoint the leak.
I found that the patch 24/7 took enough of the edge off to do the job for me. After 35 years, and at least that many tries lol. All the best, keep busy, find a new hobby