I owned an SMLE Lithgow a few years ago, which I sold. I got this rifle afterwards.
I may be wrong, but the mage well looks a bit slimmer. Is that possible, or am I just getting old?

I would be happy to cut down an SMLE mag and make it work, but I didn’t think it was the same shape.
I am not knowledgeable in the area of Lees. Hence my appeal to you folks.

Do any of you know of a sourse of short mags (5-7 round) and magazine cut-offs?

My old Lithgow had the cut-off and I agree with you. It seems to be in the way when you are using the rifle normally. But I want to get one because the old Lee had one when it left the factory, and it’s just something I’d like to have back on the rifle. Not for any practical reason.
Heck.....I hunt with flintlock rifles a lot of the time. I just LIKE them. I own an FN-FAL, and a super accurate 270 winchester I made on a Mauser, and they are way better rifles for hunting then a flintlock, but that’s not the point.
The reason I use a 1760 style flintlock is the same reason I want to put the magazine cut-off on this old gun and make a nice early style rifle out of it again.
Because I am weird!