The M1 as built has a short tender with 2 axle trucks. It looks just like the typical K4 tender but is a little longer. I know some of the M1 later got lenger tenders and some got the same ones as the M1a.
But the as-built M1 is a very nice looking mountain with a proportional tender that be like the K5 tender.
The M1a on the other hand were all built with long tenders. this was a riveted long tender.