RE: Old A&M 4.2
Look in the hub, if the crank has a small centering hole it's a Sachs, the A&M will be flush...The con rod on a Sachs crank is copper plated, the A&M is not....
VERY early A&Ms used the Sachs crank...A 4.2 MKII has the cantilever crank made by A&M..