Has anyone seen this oddball shock mount?

Get 1 from Roy and be happy.

Yup. Working on it.

That spacer came with Gabriel Hijackers to space the top of the shock away from the crossmember so they don't hit when the car jounces.

I can see that, but what's odd is there was only one spacer, and there was no clearance issue on either side. We'll file this one under unraveling mysteries from 50 years of previous owners.