Bren MkI double dovetail question

[Brit plumber]

This is an early type lower, extra machining circled in red. The Mk3 lower is similar in this area so don't get confused.
Attachment 88468

Early lower, other side.
Attachment 88471

Later type lower with less machining.
Attachment 88470

Lithgow type lower with combination of machining.
Attachment 88469

Early (Bottom) V Late type handle metal work, Blue circled shows the machining differences, red the BSA logo.
Attachment 88467

Attachment 88466

Early style gas reg.
Attachment 88465

Late style gas reg.
Attachment 88464