Then make sure it's not been done already!
An R and an SP head are quite easy to tell apart. If you take 0.2mm off an SP head you (just) run into the squish band so the "step" on an R head is twice as big as the one on an SP head.
This is of course little use unless you have both to hand.
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Please do not PM me technical questions, if you can't find it on the Forum start a thread