Looks like the Buick screws are 3/8-24 thread..
https://www.ebay.com/itm/284437335499?nma=true&si=i42gaNjfs5oTpRibZ2XXxx6KZT8%253D&orig_cvip=true&nordt=true&rt=nc&_trksid=p2047675.l2557
I think screws for the MGB have the same ball size but are also 3/8-24
