Hi, thanks for the replies: I've been sidelined with my usual health issues, now I'm back!
So, back to the engine. I've now undone the engine mounting blts and tapped them out a little, so thats good news, no seized bolts to worry about.
I've removed all the covers from the 'new' engine, the camshafts appear to be free from pits and visible wear/damage, the sump is very clean, as was the oil, and the filter again was very clean: The seller really did make a point of stopping me stripping the motor, he was adamant it is ready to fit, he'd seen it running and for once I'm going to trust the seller!
I did a few more miles on the old lump and I still love the ride...never give in!