TTBOMK, this enlarger only takes 35mm, hence the moniker.

You don't mention the Mamiya model you have. Not all '120' enlargers may work with your negatives. There are many enlargers that take 6x6 120 from a C-220/330 or folder, a few that take 6x7 from an RB/RZ and fewer that take 6x9 from a Universal/Press 23. If you have a 645 than any 120 enlarger will work.

Sniff.