Leaving the 1953 block/heads out, there are 18 head bolts on the high pressure 235s and 15 head bolts on the low pressure 216s/235s.

The internal lubrication (including supply of oil to the rocker arms) was the same for 1941-52 216/235 engines.

The 50-53 216 heads are the same as the 41-49 216/235 heads.

The 50-52 235 heads are listed as being different from the 216 heads, presumably due to the side-cover holes on the 216?