By the way to improve the stopping power of drum brakes you increase the area of the brake shoes (going bigger in diameter if possible and in width. The Chevelle and Camaro used a nine inch drum. So in the back of car mags they sell an eleven inch drum off of a big B-body car it enhance rear braking capability (even though 60% of all brake effort is on the front axle due to weight transfer on stopping.
In your case you can look at the possibility of bigger brakes off of a Super Duty Pontiac., or an late fifties Buick They were not only bigger (wider ) but cast out of an aluminum drum with a steel liner that probably has to be replaced (I don't know if that is even possible).
They were the "cats meow" when beatnicks were building lead sleds from the fifties as custom cars of the sixties. I also see them on Rat Rods frequently so they may be in reproduction. In addition to them being worn out (the steel liner being worn too far to turn again) they had a unique eight lug wheel ala
NASCAR racing of that time frame. So the face of the drum would have to me machined as well as converting it to a five lug bolt pattern. It is for this reason that I suspect they are being reproduced as a five lug knock off of the 1961-'63 race cars fielded by Pontiac back in the days of "race on Sunday, sell on Monday". Today they sell on flea bay for about $300 a pair when they come up.
Here is the front side of the Pontiac Super Duty drum:
And here you can see the extra width allowing the finned drums to stick out into the air flow to cool on roadster (these may be Buick drums or even a set of fake drums that contain a disc brake which are made for Rat Rods) .
Here is a set for sale currently on flea-bay.