Critical alignment on a 45M is a bugger. The baseboard can be adjusted by loosening the screws and shimming. There is a screw to move the head, tilt, away from the chassis. There is the ability to swing the lens stage independently of the neg, but the little ball bearing detent resists critical placement. The same is true with tilting the lens stage independently of the neg stage; this is only accomplished by tightening or loosening the bolt that the lens stage pivot on and placing a frame spring behind for tension.
I have added thumb screws to the lens stage swing and removed the ball so that the swing can be placed and stays perfectly. Also added a spring behind the lens stage and another screw so that the lens stage can be tilted. Finally I added a swing mechanism to the entire head assembly at the focusing rack. The focusing rack can swing if some hardware is altered at the attachment point to the chassis. Then another screw was added for critical placement of this swing. This is a pain to do, but now the enlarger can be aligned whereas before there were few control points. Adding 8x10 to the whole mess doesn't help, but this stage I shim to get it parallel with the other neg stage.
I realize there words don't describe it fully, but they should help with ideas on how to do it should you need to. The lens stage is the easiest one to correct.