The Singer 401A and the Singer Slant Needle Deluxe Monogrammer are two different sewing machine models, so compatibility of the cams will depend on the specific design of each machine. The shank size is an important factor in determining compatibility, as cams are designed to fit specific shank sizes. However, there may be other differences between the two machine models that could impact compatibility, even if the shank sizes are the same.
Without more information on the specific models and cams you have, it is difficult to say definitively whether your cams will work in the Singer Slant Needle Deluxe Monogrammer. I recommend contacting Singer directly or consulting the owner's manual for both machine models to see if there are any specific compatibility guidelines. Additionally, you may be able to find more information by reaching out to sewing machine repair or maintenance professionals, or by searching online forums and communities for other users who have used cams from a Singer 401A in a Singer Slant Needle Deluxe Monogrammer.