Looks like a 110 BCD, in which case you can use a compact ring set, usually 50/36 or 50/34, pretty ubiquitous these days. If you really want the 48t, you should be able to source one for this bolt pattern without too much trouble.

You'll want to verify the BCD, though. If it's 130mm, the smallest it'll take is a 38t, and you'd likely have to search high and low for a 48t.

Your FD might look a little unsuited to the curve of a 48t ring, but it should work pretty well since FDs were a lot less fussy back in the day.

No dramas with your freewheel (I can't imagine what), except if it was me I'd ditch it for a 7s Hyperglide job.