there is a new listing on EBay for a 1983 420 KTM. It appears to be in pretty good shape, located in New YOrk
skiracer,
I couldn't believe it didn't meet reserve(yesterday I believe). Nice bike and some people shy away from this and the 495 because of the cost of pistons and rings. I have an extra fresh top end for a 420 that I picked up in case I ever find a nice one in the southwest (Texas area).
Also by the guys eBay ID it looks like he is into KTM's and should be able to answer any questions one might have. Again just my take.
Ron Carbaugh