Coincidence! 2-3 weeks ago, a co-worker gave me his Beseler 45M. After having her second baby, his wife realized that she'll never get back to darkroom work, so they gave me the enlarger plus other goodies.
I didn't realize how much I wanted to set-up a darkroom. I've been hybrid for years. But this 45M motivated me to black-out the window and door in my storage room, converting it to a darkroom. A few days ago, I used it to make my first prints in 43 years.
It came with an EL Nikkor 80/5.6 (6 elements), which is suitable for 120, and I bought a 6-element 50/2.8 for 35mm (from eBay). I've printed with both lenses.
I only had one 4x4-inch lensboard (for the EL Nikkor), so I made one myself out of 1.5-mm thick sheet aluminum. I bent its corners up to make it 3 mm (1/8 inch) thick, which the enlarger expects. Works well.
I replaced the 150 watt tungsten bulb with a common LED bulb having the usual "warm" temperature of 2700K. The contrasts of grades 2 and 3 look fine to me.
You can buy a set of 3.5 inch square multigrade filters from Freestyle or B&H. I cut them down to 60x60 mm and put them into the slide-out filter tray that sits above the lens (not the huge tray in the condenser head).
My next project is to build a LED-based diffusion head. I'm going to copy Mal Paso's design that he describes in this thread:
https://www.photrio.com/forum/threads/led-split-printing-enlarger-lamphouse.173834/
Mark Overton