The fan blades are curved on the R33 vs strait on the R32. I found this tid-bit, even though it's not much help unless you know the prod. date...
"The Oil Drive problem was fixed by Crankshaft with part #12200-05U02, which was introduced in Feb of 93. Therefore, any R32 GTR produced in/after March, 93 was fixed,
while those produced in/before January, 93 were not. Those produced in Feb 93 were on the border so they could be fixed or not."