Rotten cross-member ends and missing jacking points are a pretty common occurrence.
My mechanic friend said he reckons the chassis is sagging in the middle
A 2 door saloon is monocoque - ie. the shell is structural and doesn't have a separate 'chassis'*.
Monocoque is/was a french term - in blighty the nearest equivalent is 'body shell' but monocoque is pretty universal.
(* from the bulkhead forward it pretty much is designed like a chassis - so the front end structural members are commonly referred to as chassis legs)
From the bulkhead back to the rear seat, the shell structure/strength is a combination of sills, A-post, B-post, centre crossmember, bulkhead crossmember roof and floor..
If the door aperture is distorted and/or changes shape depending on where you jack up the car - my guess is your sill construction is completely shot (and you are likely to have a rotten A-post as well).
The crossmember helps link the shell structure with the 'front chassis legs' and assuming the shell is weak, it's likely that the front chassis legs are rather more free to move than they should be as well!
In short - with a bit of thought it's possible to get the important bits lined up well prior to welding new structure in place. In reality it may be much cheaper / less effort / better end result to start with a much better shell!
Ray. MMOC#47368. Forum moderator.
Jan 06: The Minor SII Africa adventure:
http://www.minor-detour.com
Oct 06: back from Dresden with my Trabant 601 Kombi
Jan 07: back from a month thru North Africa (via Timbuktu) in a S3 Landy
June 07 - back from Zwickau Trabi Treffen
Aug 07 & Aug 08 - back from the Lands End to Orkney in 71 pickup
Sept 2010 - finally gave up breaking down in a SII Landy...
where to break down next?
2013... managed to seize my 1275 just by driving it round the block
