The 1954 cars used a 7 lb radiator pressure cap.
The 1954 trucks used a 4 lb radiator pressure cap.
While 210 degrees will not hurt the engine, I agree with Bill that a 235/261 should run cooler than that (in 90 degree weather).
Posts above have suggested many possibilities, but one possibility seems to be missing (unless I missed seeing it). Every 261/235 that I have taken apart has had debris inside the block, often being plugged at the rear of the block. After cleaning an over-heating 261 and a normal temperature 235, both engines ran at noticeably lower temperatures during the summer when idling.
