You won't need to remove the tire, for an Enfield you can just send the drum/sprocket
You can have any machine shop check that the drum is round and centered to the bearing. You can arc shoes to the drum yourself. You can looki it up but here is the basic procedure:
1) Remove the drum.
2) Put chalk on the shoes, all over them.
3) Seat the brakes in the drum and pull the brake lever, rotate the brakes a little in the drum.
4) Remove the brake mechanism. Anywhere you see the chalk rubbed off is a high spot. Use a sanding block and medium sand paper to sand that spot down.
5) Repeat steps 2 through 4 until the brake comes out with no chalk. That means the entire shoe is making contact.
This procedure gets the whole shoe hitting the drum for optimal contact. They do some more work at the shop, like cutting grooves to improve performance, but this alone will make your brakes very good.
All that said, I think you have the wrong cam bolt. Call or e-mail Hitchcocks and askDo you have someone local with an RE that you could compare to? Maybe just take it to the shop and compare to a new one?
Scott