Most Champion "R" plugs I’ve seen were the side electrode type, and I wouldn’t run them in anything but a hi-performance motor.
Antique Champion 7, or, in lieu of, the 6M or even a 5M/5MJ will give you more than enough performance and reliability to make you happy.
I don’t run modern plugs. Period. F*** ’em. For old iron, I clean up the antique plugs I find and go with it. If your ignition and fuel settings (not mix, the carb settings) are where they’re supposed to be, you can run the antique plugs for the duration of this lifetime…. and the next….
Best,
PM T2
He's livin' in his own private Idaho..... I hope to go out quietly in my sleep, like my grand-dad did..... and not screaming, like the passengers in his car...