I'm guessing that it has a Buick carb so maybe it's a Carter or a Qjet? Does it say Qjet anywhere on it?
If it's a 4 bbl, this is easy and works good for on the road and you're just trying to fix it to sell it just go with an Edelbrock. Something like this. "Carburetor, Performer, 600 cfm, 4-Barrel, Square Bore, Electric Choke, Single Inlet, Silver," available Each $350 at Summit
https://www.summitracing.com/search...Ascending&keyword=Edelbrock carb&N=4294921892
There should be a bunch of them for sale as it seems like nobody knows how to work on carburetors anymore so they all buy FiTech's so they can learn how to troubleshoot TBI fuel injection systems instead (this is supposed to be a joke).
Anyway, let us know what you have and we can maybe point you in the right direction.
Here's a place that rebuilds stock OE carbs...they might have the exact model you have so replacement for linkage, fuel lines, etc would be a direct "bolt on" making it easier for replacement.
http://www.nationalcarburetors.com/cat-buick.html
Hope you get it running and sold without too much hassle.