PT-180 QA plate is a different size then the PT-422/425.
I have heard of one case where a buyer convinced PT to weld a PT180 plate on a PT422/425 attachment. YMMV, since I am sure they will then give you some arguements about warrenty issues caused by overstressing your tractor by non-approved attachments and what-not.
It all depends if you think that you will be able to use a warrenty requiring you to ship your 12000# CUT cross-country at your expense...
I would think that the PT180/PT425 auger head is identical except for the QA plate, so it would make sense that the auger blades have the same part number (but the PT425 auger is $300 more then the PT180 auger, so maybe not... and the PT1430 auger is $600 more then the PT425 auger).
what PT-422/425 attachment are you looking at? Some of the hydraulic attachments requiring an aux hydraulic circuit (4N1 bucket, grapples, mini-hoe, snow-blower, spreader) would require you to modify your hydraulic system to make them work (well documented here in the archives).