OP, the thing about Lee Enfields of any mark is that if they don't shoot well without a scope, they will seldom shoot better with one.
Any Lee Enfields I've added scopes to and the S+K instamount is great, the scope was added because my aging eyes don't see the sights well enough to give me confidence, especially in low light conditions.
Some of the older mounts required drilling and tapping to fit bases that really weren't adequately rigid enough to stand up to field use.
The S&K bases work just fine.