Joined: Jan 2010
Posts: 9,797
Likes: 1,763
From: Northern California
Bikes: Cheltenham-Pedersen racer, Boulder F/S Paris-Roubaix, Varsity racer, '52 Christophe, '62 Continental, '92 Merckx, '75 Limongi, '76 Presto, '72 Gitane SC, '71 Schwinn SS, etc.
The Alpha designation is more about a point in the indexing era than about quality level, since there were a range of Alpha derailers of varying quality (higher number equating to higher-tier quality). I think that they topped out at the 9000 level, and the bottom level was 3040. 7000 and up were quite nicely finished.
An appropriate square-taper bb for any of Suntour's cranks shouldn't be hard to source, but be aware that at some point the Superbe and Sprint cranksets changed from "Superbe" (actually exactly equivalent to ISO i.e. Campag cartridge, and to older Sugino Mighty) taper to JIS taper in the ~early-to-mid 1990's.