You'd have to ask about very early Carbines from a collector who's "up" on that, but I've never heard anything about an early dovetail size, and I've never seen any early sight except the "L" type flip model.
I used to have the book "The War Baby" written by the #one top Carbine expert, and he mentioned nothing about any early dovetail or sight.
Since the book is THE collector's reference, and he discusses everything about the Carbine, if a different sight and dovetail was used he would have mentioned it.
It sounds like the cut has been modified.
Remember, Carbines were built 60 years ago, and have been in who knows how many hands.
They've been altered, refinished, and have had non-standard sights and parts installed, then removed again, and it's often not possible to spot the changes until you try to install something else.
In this case, what you'll have to do is shim the sight.
There are several methods of doing this.
One is to have a GOOD welder build up the SIGHT'S dovetail, then file to fit.
All that's necessary is two spots applied to the dovetail.
The second method is to make a steel shim that can be installed into the receiver slot WITH the sight.
Another method is to simply epoxy the sight in place.