Since no one has replied, here's my two cents worth. I have always used OEM magnesium cases and haven't experienced any problems. I've never used one that had the #3 plate welded, and I don't see what that accomplishes anyway...maybe email CB Performance and ask them why they would weld on a new case? Perhaps for a turbo engine?
As you are asking about an 84 mm stroke, I can give you my experience with my current 2332 cc. It's an OEM AS41 mag case and started out as a 1776 cc for a few years, then a 2017 cc for a few more years, and now it's been a 2332 cc for the last 4 years. I have just over 12,000 miles on the engine and everything is still fine...no cracks, original standard main bearings, etc (I just swapped camshafts recently and everything looked good). It has over 400 drag races, including over 250 since it became a 2332 cc. I clearanced it with a dremel, so the 84 mm crank, rods and camshaft would rotate cleanly. The bubble cases you mentioned are pre-clearanced, IIRC.
I have never used an aluminum case, but AFAIK they tend to run a bit hotter by 15-20 degrees, from what others have told me.
What are you going to be using the engine for? Street, long distance, Friday night drag racing?
