But I am still not sure of the loads... That was the part I really wondered about.

Their 5:1 system looks ideal for my application as the outhaul runs out of the boom to a cleat now... and I would just added the blocks and the cam cleat externally.

That would give me 43 lbs pull at 12 knots of wind... a bit high, but I think doable.

I would run the B and C Fiddle blocks along the side of the boom vice inside. Defender has good prices on them. It's worth a shot.