Ben Micklem wrote:
I'm looking for a reclaimed 1930's panelled front door (three tall below,
glazed above), and the one we've chosen is unfortunately cut for hinges and
locks on the wrong sides.

What proportion split between glass and panel is it. If about
60(panel):40(glass) and the glass is divided into 6 panes then that's
exactly what was fitted as original on the 1930's houses in our road.
We found a new door that matched this made from hemlock which is a hard
wood apparently - can't say I'd ever heard of it before buying the
door. We got ours from Howarth Timber in York (they have branches all
over the place), but as you don't say where you are that may not be
very useful. Probably worth noting it was made by another company and
sold on by Howarths so other suppliers may also sell them. Cost about
£90 delivered - unglazed, unpainted. The glass was about... err I
can't remember actually but it was laminated and not much at all. It
needed painting in our opinion (varnish would have been doable but not
ideal).

How compromised would the strength of such a door be if I were to slot a
piece of wood into where the mortis lock was (screwed in place maybe?),

To be honest I'm not sure how strong most doors are anyway. One heft
of the old battering ram by the police sees most frames split even if
the door stays intact. So the question is what level of attack do you
want to protect against? I think the simple answer is that yes -
removing part of the body of the door will compromise the strength but
whether that actually matters is another question?

--
Steve F