No4 Mk1 ID help needed

Hi all,
Enfield disease got me again B-)

Couldnt resist to pick up a decent no4 mk1 for little money ...


On the left side of the receiver is stamped (not e-pencilled): No4 Mk1
Butt socket left side from top to bottom:

B
1943
X30.. Serial

Forestock and bolt are matching numbers with receiver

And thats it ...

Perhaps someone can tell me more ;-)

Greeeetz
SM377Y

My notes say the "X" prefix was a late 1942 BSA-Shirley. I suppose it could carry over to early 1943.

That vintage Maltby should be a double letter prefix.

Addition: 'X' prefix and 4 digit serial #