The higher-compression "848" (3836848) head became available in 1956 (and was used until the "end-of-the-line"). From 1956 onwards, it was the replacement head for all high-pressure 235s (maybe even the 1953 Powerglide 235?).

This style of adapter was/is used on trucks with mechanical (tube) temperature sender (also available at NAPA).

Once again, let's hope Pre'68 Dave adds-to or corrects this.