It's been done, although everyone pretty much uses the Kato C55 instead of the C50. Maybe that's what you meant since the C50 is a 2-6-0 not a 4-6-2. Both mike_lawyer and victor miranda have done it. There are several long threads on the Atlas RR forum about the conversion which, IIRC, was first proposed by a member there going by the name of EBIT.
The Atlas board is closed to new posts but you can still do searches.
For example a search on "K4 c55 kato" produces this link, among others:Kato JNR C55 4-6-2 RE-RUN
Some playing with the search terms may find other threads. If you find one you like you can save it by clicking the "Printer Friendly" link and saving to a PDF file (if you have that capability). I've done that with a number of interesting threads.
Some of the relevant posts my have been archived, finding them is a bit tougher as the search times out. They have set a fairly short timeout period on the thread database so you have to do some playing to narrow or widen the search to get some data returned before things time out.
I know there were relevant posts on Railwire, but my searches here did not find them. You may have to play with search criteria.
Currently Kato C55's are available on the Plaza Japan Ebay store and at MBKlein's www.modeltrainstuff.com
John H. Reinhardt
Looking at EBIT's profile on the Atlas board lets you look at all his unarchived posts. This leads toBigger pic's for PRR K4 kitbashing-many pics!!
and the reminder in the thread that his article about using the Kato C55 for a PRR K4 is in the NTrak Steam Locomotive book for 2007 (and if steam and conversions interest you , you should have this original 2006 plus the addendums for 2007, 2008, 2009, 2010, 2011 and when it comes out 2012).