yeah heat riser will do wonders, in the cold climate. Try to stay away from pic34-3, you can run a 34 just not a -3 pita to adjust. Maybe some dual Kadrons.
do the J tubes have the heat exchanger still ?
Couple of things about Beatles, all the grounds are suspect, each light has it's own ground. If it were mine I'd swap out the German bullet fuses for an ATC fuse block.
Cold wind can enter the cabin via the dash, the defroster vents don't seal to dash well, plus fuse box and other areas, fill a big trash bag with bubble wrap and keep it stuffed up against dash in the front. Iirc there was/is a trunk lining, but it isn't air tight.
Now I want another Beatle lol