Keven, it appears that your alternator is using a shorter belt to keep it clear of the bulkhead at right. Yikes.
The inherent issue with the M30 design is the lower pivot for alternator used two separate bolts/nuts and on some boats the rear one is inaccessible. There was a 'tractor mindset' at Perkins.
For my friend's Catalina 320 I had the lower mounting bracket modified with a new rear pivot arm, now FORWARD of alternator rear leg plus a compression tube connecting this to the the front arm so a single long bolt is used instead. There's a standard sliding bushing in rear alternator leg to transfer the bolt's compression as is automotive practice. You can loosen that bolt from the front and the rear nut got a wire bail welded on to limit it's rotation.
This is a higher current Iskra alternator fitted. The leg spacing is a match to the Yanmar/Hitachi mounting scheme.