Well I bought the van, and had a look at the engine...
Did a compression test, and it was good. Found out it was only a split vaccum pipe for the brake servo, causing it lean out and not run on two cylinders.
40p bit of hose and she's running sweet.

A little bit of welding to do and she'll be ready for the MOT.
Looks like the gambol of buying a non runner paid off.
Dave