Apologies - when you replied earlier that P4 clearance wasn't in the design spec I assumed you were involved somehow.
My point about all this was that a little more clearance within splashers of steam locos would facilitate quick wheel swap conversion, something which I believe EM folk do using spacing washers, although I'm not directly involved. So no new chassis unless for another reason.
In my case, yes I would need a new chassis in P4 partly because I'd want to spring the loco, but I'd be prepared to lash out on the whole loco (as I have done many times before) because the body alone is worth having. A big saving in time over making and painting a kit body, and often as good if not better quality. I was only suggesting a bit more clearance within splashers to make it easier. My Hornby B17 needed so much taking off the inside of the rear splashers that they became like tissue paper and distorted. Couldn't move them easily as they were moulded into the boiler.
Anyway I don't want to carry on an argument which is going nowhere so I'll bow out at this juncture.
Justin, point taken about Peco but I wonder where this leaves us with the 16xx? Wait and see if the wheels will fit I suppose. If not, scrape and hope!
Regards,
Bob