Source for Slant Six Distributor Wrench?

There was one. Vim № V-103, very useful for reaching the other bolt (the one on the underside of the distributor, holding the plate to the distributor body), so if you "ran out of room" on the slot for the plate-to-block bolt, you could gain the adjustment you needed.

That wrench is no longer made, so either you find one NOS/used, or you bend/weld your own.
The Snap On wrench I have is a dead copy of that.....or the other way around. lol