hi, if you were a rivet counter, the Tamiya's stock M4 sprocket wheel is for T84 tracks. The T66 tracks' sprocket wheels are slightly different.
Else, it doesn't really matters.

T66 comes in two variants (as what I know), with (like IMPACT's) and without (like KK's) the intergral grousers.

If you had the books on M4 Sherman variants, you should be able to tell quite easily.