new "exact fit" alternator doesn't fit

I have a square-back in my 65 SB (273) on after-market chrome brackets. Search my posts for photos. As I recall, the fan belt is on the inner alt pulley groove and runs direct to the crank pulley (2nd groove?). The water pump runs with the power steering, but that is all later stuff (alum w.p., short alum pulley, Federal p.s. pump). My engine has the factory damper & 2-groove crank pulley, with separate alum AC pulley insert (dealer or after-market kit).

Anyway, lots of ways to mount and drive an alternator. The square-back is better, spec'ing ~70 A output vs 30 A, and is much better at low rpm. To use it electrically in your car, ground one of the brushes. In my car, I mounted the later Vreg near it.