With a 216, the centre to centre measurement on the carb studs is 2 11/16". That measurement on a 235 is larger.
If you remove the carb, the bore at the bottom end will be 1 1/2" for a 216 and 1 9/16 for a 235.
If your motor is original, it will be a 216 and the valve cover will be held on with two studs coming through the top of it.
If you have a side cover that does not go higher than the block, your casting numbers on the block and the head will be the same for the 216 and the 235.
