You are asking a lot to be honest but surely........ All you need to do is to borrow your pals deactivated Mk1 Bren and take the necessary measurements from that for what you need. And in doing so, you'll have something that is pretty close to realistic

I'm not sure that anyone in Englandicon - or at least anyone in their right mind who savours their freedom would give out the engineering drawings to make a Bren barrel and body. Only my view of course