Hi all can anyone tell me how you know if the heads have been modified to take unleaded petrol.The heads are off a 1200 but with a big bore kit put in.Don't know how long ago but I'm replacing valves and springs.

All the later (only coz I'm not sure about the early Oval stuff) ACVW heads are unleaded compatible. They have steel seat inserts into the alloy head material.
Some of the very late '70s models used special valve stems, but they aren't needed normally, just with lean-burn '70s injection stuff.
If you are replacing valves then possibly consider a quality performance part (Manley, SI Valves, CB swirl, etc) and good multi-angle seat since you need seats re-done anyway, it will give you a big boost in performance for not much extra, and the valves last longer too.
Springs and also collets can be complete rubbish even brand new, again, buy a quality brand (Crow, Comp, even OEM VW Mexico) in preference to most aftermarket stuff if possible. It definitely makes things last longer and vastly easier to set tensions evenly.