Just to update - I have now found that the pistons are Henry Abe, but have a shorter life expectancy than the wheels! Next step is a bit of a stop to take stock kind of thing. Remove the two valves which refuse to slide out because they have been splayed by the colletts, then get the head and barrels degreased, masked and bead blasted, then sent to NBS for an opinion on the state if the bores and by association the pistons. If there is any doubt then the 810 Abes will go in the bin and I will have to save up for some Wiseco 836s. Then the fins on the barrels can be repaired where someone in the past has removed all but one or two of the retaining nuts before giving it beans with a tyre lever to fail to get the head off. At the same time I will get the wheels bead blasted and see how they look. Meanwhile this evening I put the impact driver to good use and removed some horribly chewed crosshead bolts off a casing which has been painted matt black and will be blasted and polished. Underneath I found lots of oily things which looked like bearings, springs and linkages. So they will get left well alone by me and left to Nigel at NBS to disturb, and only then if deemed essential!
So that's the next few weeks taken up then....