I am looking at a set of belts I removed from a FFR S3 cartridge , probably one of the last recon units although it if IIRC 3mb not 5mb (they would be remanufacture with contractors too). Thw plastic bag is still heat sealed.
The fan belt - Land Rover 614670 Made in DENMARK (it is genuine ) need to check but almost certain the part No. correct , also marled 42 and 7042 , I would have to measire - probably a 42" (inside) , the Section is standard (car) 'A'
In later year they moved to a COG belt as they run cooler, last longer without stretch and transmit power better. The data is Continental , so - CONTITECH (trade mark) CONTI-SF AVX13X 1325 La , so I decode that as 'A' Section 13mm wide (IIRC the small width being 7mm) with a internal length of 1325mm
Having said that - my understanding is that the 1325 is OK and workable but in fact not the exact length that is best. I have some old notes and think this equates to 514570. A S3 FFR engine is identical to a S3 Lightweight engine of same date manufacture - a typical Solihull record states 535688 for 1977 manuf.
You could buy a belt or two from a Factor on sale or return - fit and tension and I would say you need to be at shortest so scope for plenty of adjustment. It could be that ABRO on view cog belts don't stretch opted for a median ?