Ah, the tension part....didn't think of that. I've got a bunch of recip. blades in the shop, all sizes and tooth counts. Now I'm wondering if another recip. blade would make a good spine. They are stiffer than a hacksaw blade and would provided a spare. I'll build what you built to better understand what you were up against.
Once perfected you need to submit your design/instructions to the make-your-own gear section. It's a good idea!