Correct 1972 Porsche 911T fanbelt doesn't fit on my original matching numbers engine

[SpawnyWhippet]

I ordered a service kit from Sierra Madre to service my '72 911T. It came with this fanbelt:

999.192.176.50 Alternator V Belt (65-89) Genuine (9.25x710mm)

It was slightly too short to fit on my fanbelt pulley, so I checked the old one (which was slightly too loose when all 6 shims were on the outside of the pulley) and it was a 10x735 size.
Am I installing it wrong, or does anyone know why the correct belt is too short, and which one I should order?

[BrentF]

Dumb reply perhaps, but have you spoken to Sierra Madre yet about the mismatch? BTW: I have a tune up kit on order from them.

[edmayo]

I think the original was 9.5 X 710, but many of them now come in at 10 X 710. Either of those should fit unless you have some weird kind of A/C pulley.

[SpawnyWhippet]

I do have an A/C pulley fitted, so you could be onto something there. I called SMC and they advised me that 9.25x710 was the correct part for my car, so it must be a dealer supplied AC pulley when they fitted it in 1972?

[SpawnyWhippet]

Update, I added another couple of shims to the pulley and this tensioned my old 10x735 belt sufficiently. It would be a better fit with a slightly shorter belt and the correct number of pulley shims though. I guess a 10x725 would do it perfectly.