I'm not actually disagreeing with my buddy Bart here but....... it really depends on the attachments in question.
If the mower deck is a 44" cut width, then it is fine for a 400 Series tractor.
If the push blade is also a 44" wide model, it too can be used on a 400 Series tractor EXCEPT in full angle position. It is fine for straight pushing or angled left/right in the first hole on the positioning plate. If you angle it fully, then your rear wheels will drive over the spoil that comes off the blade.
If the snowcaster is a 38", it too can be used on a 400 Series tractor by adding a pair of "wings" to widen the cut 4" in total to a 42" cut.
This all comes down to how cheap you can buy the attachments. Tell us what he has and what he's asking. If you have photos, so much the better.