as justin said. if it's off teh car, bit of tippex on the splines & case of the output and teh same on the prop flange and case and start counting.
input shaft will either turn just under 4 times (3.9) just over (4.1) or about 4½ (4.444) for every 1 turn of the output shafts.
if it's still on the car, disconnect the prop, mark the input flange as above, then put a bit of tape on a rear tyre and with both rear wheels off the ground, rotate the input shaft
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