1964 plymouth valiant Slant six to 340

Early Dart has a 111 inch wheelbase vs. the early Valiant's 106.5.

Speedo gears for the early trannies are no longer being produced (unless that's changed since I last looked), but you can find one every now and then on ebay or at swap meets. I have probably half a dozen, with various teeth counts. (None for sale.)