Hello dstrecker:
Here is some food for thought on this problem, I have some background in traditional millwrighting techniques, and in an 1846 Mulley Mill that I was entrusted with to keep in operation, the large guides that house in the head blocking mechanism were held in place with wedges instead of pins. These wedges were tapered to pull in tightly the guides whose ends were motised through a large timber. I see no reason why with a mortising chisel you could cut away and fashion a tapered rectangular hole through both the tenon and the timber and use a hard wood wedge to pull the scarf together. I hope this helps--NH
