Mallory used to sell a round-bottomed coil that actually said "The BEST coil I ever made, M. Mallory" right on it. I have one with the matching dual point distributor on my hot rod engine, and can't dispute his claim.
The Bosch is also a good choice and probably a little easier to find.
my 6volt coil died had an old one as a spare and fired rite up,its the modern type what the best coil for replacement..thanks guys
Here’s a picture of one of the coils that Tubman speaks of. I’ve never tested it, but I saved it cause it looks cool too.