You only have a choice of adding an inch into a P11 set of primaries, or removing an inch (?) out of a Commando set ?
Beats me why there is nothing suitable (?). Ariels, Enfield and Triumphs and (many) others have had alloy primaries for many (decades). 100,000+ Nortons could have benefitted - and thats just since WW2.
Probably wouldn't be that hard to get a set cast up using the tin ones as patterns, suitably prepped. Do a spare thousand , they will probably sell like hot cakes ??
Re: alloy primary covers for an atlas
#319898 06/23/108:38 pm06/23/108:38 pm
A friend used G15 alloy primary and rather than cut and weld on the primary, simply made new rear motor/ gearbox mount plates. It was much easier than modifying the covers. He used a set of G15 plates and Atlas plates overlaid to trace a pattern for a new mount made from 1/4 inch alloy.