Hi Steve. To add a little more personal comment to my previous post.
If you are restoring for someone else there a certain decisions to be made concerning your time, your costs, hassle etc. Also the use the bike will be put to. A factory perfect rebuilt will cost a lot, look nice, and you will be scared to use it lest you dirty it, come off it or it gets nicked. This may be what Josef wants, but it will cost. Sometimes it is better to build up a sound, working but not mechanically perfect or concours finished bike which can actually be used. Second hand used genuine parts and cheap paint is the way I would go if I were only doing local runs for leisure/ pleasure/ club runs. In other words get it a runner and get some fun. That paint run and a bit off rust are not seen at speeds of over 3MPH.
Now back to your specific problems. No wonder you are confused. On your original engine there is a bit missing, namely the oil slinger, part67-349, described in the parts book as a bearing shim. It is and it isn't. Yes it is a shim near a bearing, but it does not locate the bearing. It rotates with the crank. Someone has removed the bearing at some time. There are two non standard holes drilled in your case, which hopefully coincide with the outer race. You lucky man. A small punch will enable you to knock the bearing out, but never be tempted to do it cold. Warm the case in the oven, on the barbecue, over a camping stove, blow torch until the spit dances when you gob on it. The race may drop out. or knock it out squarely. To replace put the bearing in the freezer overnight, heat the cases as before and it may just drop in or require a light knock with a hammer and a block of wood.
The missing shim appears in other posts so you can find what you need.
How badly damaged are the original cases? Looks that both sets need welding. If possible I would stick with the original cases. Firstly it would be nice to keep the whole ensemble together,, and may be easier to register for road use. Secondly, you may already have the scroll type drive sleeve which will save you a little bit of cash. Thirdly, welding missing parts to castings will cost, repairing missing thread sides is a lot easier. Find a local gearbox reconditioner, ask who repairs their alloy cases, or search for aluminium fabricators. These guys are usually pleased to do these jobs if you catch them right as it adds challenge and variety to their day. Suss them out first and be honest in what you need doing. If they make it clear they will not help, fine, leave on good terms as they may be just having a bad day I pay them in cash if asked, bottles of beer if they don't. Treat them right and they will do you a good job.
Ain't that right Musky?
Keep on spannering, Swarfy.