I agree with both of you and if Hornby haven't designed the upgrade into unfitted models then, yes, sounds very difficult involving major works on a new model and blowing up the guarantee in the process. I was asking on the basis of the Sam's Trains LMS B5 review where he mentions the space where the atomiser would sit on the chassis but I didn't appreciate there would be a synch wheel needed. So I guess if this feature is a success there might be an LMS version in a year or 2, meanwhile I could get the P2 thus equipped and just run a guest train of LNER stock (but it's a lot of money!)