How do you install an LM3800 when there's only 6 inches between two 9x8 door tracks, with drums too big for the machine to run? This is how. Sometimes, the customer knows better. I could never understand how someone designs a large three car garage, and spaces the doors less than a foot apart.
I made a crude bracket out of 2x2 steel angle and some 14ga punched angle, jig sawed an adjustment slot into the mounting flange, and bolted it up directly to the track with knurled bolts.
Using a sprockets from the LiftMaster 480LM alternate mounting kit, and a few feet of chain, I had it running quite well. I wouldn't stand under it, though.