Doing it without a really big enlarger will be difficult. Even with a 4x5 enlarger, you'll be able to fit only about 6 (maybe 9 if you really squeeze them in) frames of full frame 35 mm negatives into the carrier. I question the need for doing this with medium format negatives, since they're big enough to be evaluated easily with the naked eye. OK 645 might be a little too small, but just a little.