Thanks folks for all the advice, I really appreciate it. To answer the questions that were raised -

Clayton - Yes, I have a mast head halyard for the spin / reacher. No running backstays though. But that's how the boat was built. I'll take my chances without them initially since I have an extra mast. I do have a similar cable running across in front of the bridle for attaching a reacher, but it's only 6" in front of the bridle.

Carlbohannon - Since I'm planning on attaching the sprit to a separate crossbeam that sits in front of the beam that the mast sits on, a 6' sprit would put the end of the sprit 11' 8" in front of the mast. I can go up to 7' though, and down to A 3/16" wall, it can always be made shorter. 7' is the limit for UPS I think, there is no tubing source nearby.
I was planning on mounting the tube to the beam with a bracket, a cable straight down from the bridle 69" out, and a cable up from the end of each hull running to the end of the sprit, or near the end. The tube breaking before the mast does is reassuring.

MauganH17 - Thanks but I'm trying to do this on the cheap. I bought 2 boats and hauled one to the dump so I have plenty of shrouds, blocks, turnbuckles, pad eyes, etc. Everything except a pole ($50 at onlinemetals.com) and a Harken 3049 furler which I can't find cheap anywhere. They're too new I guess.

Avalondarlyn - Wow, nice ride... Really nice. Your suggestions make sense but the compression post has me baffled. Is that the white rod running up to the bridle? If so, I was planning on using a cable there to hold the sprit up, and a bridle to the end of each hull to hold it down. Is a post necessary to lighten the load on the bridle at the end of sprit?

Thanks for all your comments and suggestions. I couldn't do this without you folks.

Matt