Here ya go, a conversion that BSA used to do many years ago. If you look very close you can see where the rear sight spring hole was welded up, the bluing is not uniform. From experience, tapping the heat affected area for a scope base screw can be a real bear, the 3-1/2 per cent nickle steel alloy gets very hard when welded. This is the real reason why I like the Remington actions, there is no hole to weld up!!!!

My last Enfield job was some 20 years ago, only photos I have are on 35mm film.

And, one thing the BSA guys failed to do is mill out the charging clip recess, do not need it on a sporting rifle, it looks awful, and the sharp points will cut your fingers. I mill all the way to the rear opening of the charging slot, and continue the milling down to the same height as the right rail, using a 1/4" diameter carbide end mill to give a nice radius at the junction. That truing arbor in the above photos has a lot of uses, I also use it in the milling machine to hold the action in conjunction with a dividing head when I am radiusing the rear bridge and milling out the charging clip slot. You will need the extra length in the ejection port anyway for the big cartridges like the 510 Wells.

When I used a Winchester action and welded up the hole in the rear bridge, I would use a piece of 4140 ground for a snug fit into the hole with a little metal sticking up above the bridge, Then a TIG weld with 3-1/2 per cent nickle steel welding rod (get it from Brownells) all around. Radius the bridge a little over size first, weld in the plug, then accomplish the final radiusing and polishing. Use the same rod for bolt handle welding. Cut the bolt handle off way down on the shank, you want the weld as far as possible from the main bolt body. Be sure to use a copper heat sink inside the bolt and wet rags to keep as much heat as possible out of the bolt body.

And forget about tapping the side of the rear bridge for a Lyman or Redfield type sight, they are far too fragile for a big bore stopping rifle.

The floorplate on the BSA has been flattened but not hinged.

Current rumor is that BSA sold a lot of the converted Enfields in Canada, so a search of gunshops in bigger cities might turn one up.