I would like to buy my first British Bike

[JohnC]

I am told it was first registered early 1960, so it could easily be a slightly earlier model. I keep reading that the crankshaft bush/bearing can wear out on these bikes, I am not used to British Bikes, how can I tell what is normal engine noise and what should be a real concern? I think I should be able to spot something with a really loud /   terminal bottom end knock, but it's going to cost me if I miss spotting something worn in the bottom end.

[Rocket Racer]

Yes the timing side bush is the weak point on these motors. More an issue as engines were tuned (in the later unit twins) and the bigger 650 capacity, but all these bikes can still be unobtrusively worn. I have a couple of mates whose A10 purchases both ended up needing a full rebuild.
But likewise with clean oil these motors will run big mileages.
The upside is these engines are easy to work on and parts are readily available.

Once the timing bush wears, oil pressure to the big ends is reduced and all bets are off.

[muskrat]

The only way to check is physically. With the timing cover removed a screwdriver between the shaft (lock nuts) and oil pump or inner timing cover, movement up & down and fore & aft can be checked (dial gauge is best). End float can also be checked. 0.002" in any direction is acceptable, more than this is indicating a freshen up is not far away.
In saying all that I've seen figures 3X that and still ran well with very little noise. (Might have been the xtra thick oil he was using  )
Get it running, check oil is returning to the tank, after a few minutes you should see air bubbles in the flow.
If it all sounds good, ride it like you stole it!
Cheers