Sometime in the early 70s. I need to go all the way through it still. There isn't any wear on the cylinder walls. I haven't inspected any of the crank journals but I assume they'll be pristine.
I'd like to replace the heads. They say that the aluminum heads from HOT HEADS flow really well. The pistons need to be changed to drop the compression and I should put in a new camshaft optimized for the blower.