First suspicions are the colour. It has been resprayed to modern metallic BRG and the underlying shell colour is green (under carpets, behind dash etc). I do not recall dark green Minis in 1980, could be wrong on this though.
The seats and interior trim are certainly not 1980, I enclose a photo detailing the scheme for seats and panels. Can anyone identify it? Was it a special or anniversary edition? This was probably the donor or is it the original?
If the body is correct then it appears as though almost a complete engine, loom, interior transplant has taken place and you have to ask yourself why?
If anyone can suggest a difference between 1980 shells and those from 1990 onwards which I can use to get piece of mind I would appreciate it.