The OP says this Model 3 version is built into the same external housing as the Model 2. If you look at the Model 2 on his website:

Modern Enlarger Lamps, Model 2

you can see the Omega-specific 4 horizontal bars that match up with the raising/lowering carriage assembly unit unique to the D-series. It's not a circular Aristo-style drop-in. However, since I don't own a Beseler 45MX, I can't say if it might be adaptable or not. I'd be curious if you think so...