What year 235 fan?
I'd go with your 1947 standard 216 fan, which I think was 16 1/4" diameter.
But if you have the 18" diameter 4 or 6 blade 216/235 fan blade, use it.
If the above information does not help, use whatever blade that does not hit the radiator (and/or, does not hit anything else). The most important thing is that the fan blade is located correctly relative to the radiator - the relocation/adaptor plate takes care of that.
