Hi, please can I have tips for installing a door lining in a new brick
opening in a old uneven/sloping/unsquare/untrue/twisted wall.

My ideas are

1 Assemble the lining and then lay it on the door and try and brace it
to prevent twisting out of true as it is lifted into the opening, or

2 place the the door lining in the opening then lean the door against
the lining and then marking the location of the now 'aligned' lining
on the brick opening and fixing.

I will have a wooden brace temporarily fixed across the bottom of the
lining to keep the opening distance the same as the top of the lining.

Many thanks.