Thanks again Dave for pointing me to K & K. Was cheap and quick and had what I needed. Just had to brush off a little rust (Gee, I wonder why everything was so rusty?)
Anyway, spent AGES with the cutoff wheel cutting plate. Definitely not the right tool for the job, at least if time is any concern whatsoever. But I got there. Bracket is probably halfway done, but good enough to tack it together:
And bolt it together:
Looks like it might actually work out! Belt seems to line up OK, so I wont bother slotting the bolt holes to make the compressor adjustable (this makes me happy). Got the fancy car occupying the garage while its raining, otherwise I'd still be out there. Hopefully tomorrow I can get the tensioner on and be back in business.