radiator core ???

[Chamberpains]

When I've recored radiators in the past all I've used is cork board type gasket material. You can get it from auto parts stores or radiator places. I never had a problem with leaks. Just make sure you replace ALL the many many bolts that hold the side tanks on and make sure you use a torque wrench and go around it couple times with an hour or 2 waiting period between checks. I also used lock washers that didn't come on the factory bolts. IMO It's time consuming but worth it. You don't want to over squish the gasket or have the gasket material relax after you put the frame work back on. Also it's great advice from Rawze to replace the foam and not stress the frame on to radiator (within reason) they can be a bit temperamental with new foam and will relax after its in the frame for awhile.

*** edit
I used RTV silicone at the seams and corners of the gasket.