I wish you well. We had an 2006 1150. I also went through this same learning process with installing a high strength bolts and drilling out the coupler connection as you describe. We also broke many bolts over time increasing bolt sizes with grade 8 hardware. Once we got that connection to quit breaking bolts the last motor broke an internal gear. We ended up finishing our Alaskan trip by manually opening the slide and wedging a 2x4 block inside to keep the slide closed in travel. AF was useless helping to ship a new motor to us. A dealer quoted us $800 dollars to ship one out.
I did a write up hear back in 2006-2007 replacing the first broken motor. I did a search and couldn't find it.
Hopefully your fix's results won't mirror ours.