Exactly which window are you looking for? I have street side and curb side slider windows available from a 345.
I do know the 345 slider windows are slightly shorter in height than the same style of window in an Argosy, at least on my 20' Argosy anyway. I believe they are the same width, just different in height.
Air forums # 1674
1974 20' Argosy Motor Home
1974 31' Excella trailer (parting out, as of 4/1/2015 I have wheels, brake drums, windows & holding tanks left to sell)