Crikey, my post was perhaps useful. Ok then, let's deal with the shim issue first. If you erect all the parts of the drive side on to the crank, and leave the spring off, you can study the action. SRM are almost right, but the 'hammering' action is there even when the nut is fully tightened. The BSA system is flawed. My (hopeful) cure is thus: Firstly, the shim needs to be a single thick entity and not a lamination of several thin shims, and secondly, when mounting the bearing, the shaft and bearing and shim need to be SCRUPULOUSLY clean, the shim and the bearing is assembled to the crankshaft with a 'permanent mount' grade of loctite. The bearing is immediately clamped in position with a suitable tube spacer and the crankshaft nut fully tightened. I mean really tight - hammer blow tight. This is then left overnight at least. This is the first job I did when erecting the engine, and it is deliciously easy to get it right when the crankshaft is gripped in the vice, and not arguing with you. Sidecar outfits put enormous loads the shock absorber - I am happy to report no further problems, and I don't anticipate any. I still have my fingers crossed though...I have been too long in this game. :-).
My bearing conversion is a bit unusual, and a bit difficult to describe. I doubt it would ever be commercially viable because it involves some tricky machining, but it works very very well, and that is what matters as Einstein would say. It involves machining the cases to accept a substantial bronze bush, which in turn houses the needle bearing, and the tricky bit, a very narrow double piston-ring mechanical seal, the oil being fed into the crankshaft between the two piston rings. The whole seal is approx. 10mm wide. The leakage thru the tiny gaps in the piston rings lubricates the bearing/crank thrust face, and the timing-chest.
I wanted to retain the crank thrust face for several reasons - it is robust, it provides the extra length for the enclosed components, and (perhaps best of all) it can be fiddled with to ensure a decent thick shim on the drive-side. It might even be possible to arrange for no shim at all, but I have not explored this. I never will in fact, because the last conversion left my workshop some time ago - advancing years and a few little strokes have taken their toll. I hope this post will prove useful. Best wishes.