Degsy. Simple answer is that these are pattern parts, supplied to the nearest approximation does it really matter size. As you can tell from the design, the clutch basket sorta floats against the thrust washer and any length of roller exceeding the shoulder on the clutch centre will result in seizure. Too short is fine. Too long, it won't work.
Jimbo's right, and regrettably these infernal items will be firmly embedded in the aftermarket new replacement parts supply chain. If the originals look OK, use them. Plunger clutches always have an element of rock, the lateral support for the chainwheel is poor so don't expect perfection. NOS rollers if you can find them are the best, old used originals preferable to don't work modern pattern ones. If you bought from an established reputable source, request a refund as they are not fit for purpose and the seller should be made aware of the possible damage to his reputation. They may be selling these items in good faith, unaware that they don't fit because the majority of punters don't complain. So the old "No one else has a problem" ain't strictly true. The originals are a size of imperial rollers with a good chance being available from your local or internet bearing suppliers. They're nothing special.
Swarfy.
