Window Replacement 1986 16' Scamp

[GriffPete]

Hello!

Long story short. I bought my Scamp a little over a week ago and am putting together my rehab list. The windows leaked (large rear window, passenger side and driver side farthest rear windows) so I have temporarily sealed them knowing I'm going to take them out and repair/replace the windows and seal with new Butyl tape etc.

My question is, does this window installation look like a modification by the PO? Also it looks like the PO has installed furring strips all around the interior to hold the foam board insulation they installed. I have searched here and seen rivet secured windows, screw secured installation, but this seems to be a mod to accommodate the wood framing maybe? Wondering if it would be better to order some new windows from Scamp as these windows are pretty well shot (disintegrating pane seals on outside and in, slider tracks/channels are warped cracking and non functional).

Sorry for the crappy pictures. (tried to crop the bigger pictures I had)

Thanks for any info/help/suggestions!