Something like this? A syringe and some lacquer or nail polish. I haven't tried it, but it seems to be a good idea.
https://67-72chevytrucks.com/vboard/...d.php?t=690408
EDIT: I bought Trim Parts 350 emblems. They are dead ringers for the originals except for being slightly thicker. I assume the 400s would be equal quality.
https://www.trimparts.com/9617