"...grind off the back 1/3 of the receiver, and taking the scope mounting platform with it. ..."
There isn't really a scope mounting platform, sounds like they ground off the charger bridge at least, and maybe the rear sight, replacing the latter with a rear sight on the barrel?
That's a shame, because one of the easy options, though it is not the best, is the Weaver TO1 mount which needs that charger bridge, and most of the designs that avoid drilling and tapping rely on the rear sight mount. If your receiver still has that, it is a simple option. The drawback is that you lose the rear sight (can be put back, though.)
You might find a Parker Hale side mount, which will require drilling and tapping on the side of the receiver. They have been out of production for years so you need to get lucky on the secondhand market for that.
There is the Cad-Technick mount, which screws on at the safety and the ejector screw hole, no gunsmithing, and it comes apart to allow removal of the bolt and use of the iron sights, which remain in place, and retains zero when you put it back together. The downside is that the scope is mounted rather high, so you need some kind of cheekpiece on the stock, it is one of the more expensive ones, and as far as I know is only available from U.S. sources (e.g. Brownells). (This is what I use.)
Have you tried the search function for this website? We have covered the topic of Enfield scope mounts a few times.
