Look in the salvage yard on SBCs in cars like Buick, Olds, & Pontiac where the TH350 was also used. You'll have to modify what ever you find, unless you run across a 250 in one of those cars.
I have occasionally seen a 67-72 C series with the 250/350 combo, but their pretty rare around here. That cable on the other board is for a 2004R NOT a TH350. They MAY set up a little differently.
best wishes,
Les
