if its the b18 (by the year 1963, it should be), there are reproduction aluminum radiators. i bought one like this a while back for my p1800 and it seems ok.
https://www.ebay.com/itm/50MM-Aluminum-Alloy-Radiator-Volvo-Amazon-P1800-B18-B20-engine-GT-1959-1970-M-T/313317405401?fits=Make%3AVolvo&hash=item48f32c32d9:g:O5IAAOSwZB9aH7HT
if its the b16 nose, i managed to get this civic radiator to fit my 61 544 with a little modification (it has a b18 engine in it now):
https://www.ebay.com/itm/401588152860?chn=ps&norover=1&mkevt=1&mkrid=711-117182-37290-0&mkcid=2&itemid=401588152860&targetid=1068323858830&device=c&mktype=pla&googleloc=9028303&poi=&campaignid=10454522096&mkgroupid=104612011900&rlsatarget=pla-1068323858830&abcId=2146002&merchantid=6313274&gclid=CjwKCAiA65iBBhB-EiwAW253W8VLagu50e4hp6xzCIrfhwZrSqfyvvukMy4hN1hjLiLGEW4F1YUjwRoC0iMQAvD_BwE
Of course if you want to stay stock look, then the usual suspects can supply oem radiators.
dean
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