Mk2 doors will physically bolt up to a mk1 no problem, and vice versa.
The differences come with the window regulator fixings and the door release handle. Mk2 motors will NOT fit a mk1 door without modification. They look almost the same, but the two locating brackets are in different places, plus the electrical connector is slightly different. I know this as I have a set of mk2 motors that won't fit into my mk1 doors!
However, I'm looking into the possibilty of having the brackets removed from the regulators and rewelded in the mk1 positions. Not 100% sure if this will be possible, but when I get the time to do it I will report back.
Of interest, I have just bought two pretty good mk1 drivers doors for my mk1 Uno (no rust on the bottom!). One of the doors has the holes on the inside frame to take both the mk1 AND the mk2 window regulators, plus both door release handles. The other one, like the doors already on my car, only have the mk1 one fixings.
I read somewhere that the last of the mk1's had fixings for both. Maybe the mk2 doors have the same? I have a slightly rusty mk2 door in the back garden but I haven't removed the door trim to check.
This is kind of my dilema, as I have a mk2 turbo interior that I want to fit to my mk1, but that will mean I will have to cut extra holes in the door card to make them fit my mk1

My passenger side door is totally rust free, and is for mk1 fittings only. One of the new drivers doors has more original paint (both the same colour as mine!) than the other, but mk1 fittings only. The other door has had a lower part respray, but has fittings for both. But that doesn't get round the problem of my passenger door being mk1 only...
Anyway, when I've decided which one I'm going to use, the other drivers door will be up for sale for what I paid for it. Thing is, I offered Jai (Turboned) first refusal, so if he doesn't want it you're welcome to buy it off me.
By the way Oldskoolmk1turbo, is it the WHOLE door you can get for £50 new, or is it the outer skin only? £50 for a brand new door is very tempting! Last time I looked up a panel supplier, the lower repair section was £15, and the door skin (not including the upper window frame) was about £45. £50 for a whole new door would be brilliant!
Are you going to the ACE with your new turbo this Thursday Bushboy?