All 216 exhaust manuals went straight down, and 235 exhaust manuals went straight down through 1949.

All 1950 and later 235 (and all 261) exhaust manuals angled rearward.

1958 and 1954 235/261 exhaust manuals will interchange.

The 1953 exhaust manual might attach to the later heads - maybe someone else can confirm this (are the ports the same size?)?