Based on what Doug said, if you cannot get a motor that doesn't require a lot of adapting, try and find the bearings for yours. There was a thread awhile ago where an OP replaced the sleeve bearings in his Coleman/FASCO motor with ball bearings. Sounds great, but sleeve bearings are used in fans because they're quieter than ball. In an RV A/C I don't know how you'd hear the difference over the roar, though...
If you're actually in Houston, you've got to be able to find a motor rebuilder or a bearing shop. It'd be my choice to repair a working motor than cob up a mounting for a new one. That said, if you made up some brackets, an epoxy like JBWeld would hold them to the new motor without welding, drilling, riveting, etc. Just remove the paint, rough up the surface, and re-paint before installing.