[FWB]

wrench,
your info says you have a small block, is it a big block or small block you are having the trouble with the t-stat.
if it is a big block the early t-stats were large and i believe 67 and up were the smaller diameter. if you need the smaller, a ford pickup with a 360 or 390 would be a good application to use at the autoparts store, say 1974 -76