Mac motor ID needed

[Jeffrey Sligh]

Trying to figure out which motor this Mac is, I'm thinking it is a 91, but I'm not 100% sure since I'm not fluent in Mac. Didn't see an engine area on here, so I figured I'd put this here since I know the motor was bought before 1972.

Flywheel side:

  IMG_20200203_162038.jpg (Size: 1 MB / Downloads: 19)

Dual Carbs:

  IMG_20200203_162124.jpg (Size: 1.11 MB / Downloads: 10)

Clutch side (BTW, which clutch is this? Horstman?):

  IMG_20200203_162547.jpg (Size: 1.12 MB / Downloads: 14)

Back of the motor:

  IMG_20200203_162616.jpg (Size: 1.42 MB / Downloads: 11)