many years ago back in the late 60's there was a firm that did a pure needle roller conversion that had a thrust washer made from phosphor bronze fitted to the timing side and all the bronze bushes were replaced by needle roller bearings, this was before devimead did it, i still have this engine in my loft, it was highly tuned with a polydine cam, 9:1 pistons, gardener carb and many other mods and it went like the clappers, no low down power and a very rough tick over, but it is still on that original needle roller timing side bearing, one major problem with fitting needle rollers to the idler shaft was oil getting in to the dynamo as there was no seal, nowdays you can get those bearings with a seal built in so that would cure the problem. building another engine on simalar lines but with a 357 cam instaed of the polydine as that would be dificult to ride in modern traffic.