I thought this one would be easy, but my Googling has failed to turn up the tool I describe. I did not realize these were obscure. Tons of spreaders online, just not the right type.
The most popular separators are clearly made by KD or Lisle, both of which are more of the c-clamp type. The 'scissors jack' type is superior and more versatile.
I have 2 of them. I bought one over 10 years ago at an auto parts store, and the other at a yard sale ($2 Woo-hoo!, I'll take it!). The yard sale one is my favorite, as it has a nice big screwdriver handle that you turn to expand or contract it.
I'll look for a brand name on these, and see if that helps tweak my search any.
1986 300E 5-Speed 240k mi.