Hello Murray,
Though I haven't enlarged 8x10 negs for quite some time now, my solution was to use my 8x10 camera as the "base" for the enlarger. I custom designed and built a platform that allowed me to securely attach the camera to it with a raised box (if you will) right behind the rear standard that held my 12x12 Aristo coldlight source. I, also, designed and built a "back" which replaced the spring back of the camera. This unit held the film against a single piece of glass (to help with film flatness) and actually clipped onto the back of the camera just like the regular spring-back.
Load the film into my custom holder, slide the light source into place against the holder, add a process lens, a magnetic wall easel (Wisner sold these at one time) and some paper, and you're ready to roll! I tried to be as accurate as possible with alignment between the camera and the wall, but I didn't use anything like a Zig unit, or anything like that. Once the camera was squared up I used a couple of identical length boards to position the camera platform with respect to the wall. Since I never made a print larger than 16x20 I guess the alignment wasn't a big deal once the lens was stopped down a little.
Typing this makes it all sound way more complicated then it was...a few days work figuring out the design and, then, doing the woodworking...okay, I admit, it was maybe a few more than a few days, but the cost factor was minimal.
Good luck. Let us know what you finally end up doing.