So this morning the forecast was good (sunny all morning), so decided to crack on and get the rest of the subframe, driveshaft etc all put back together. New oil and filter, removed the plugs and disconnected the coil. Turned over the engine with the starter until I had oil pressure reading. Then installed the plugs and reconnected the coil and went for a start. Sadly no change at all in the noise which was really loud on startup. Interestingly it did quite down when the engine had been running for a few minutes, so as per Tim's suggestion, I a going to put this down to piston slap, which is a bit of a pain as that probably means rebuilt engine with overbore I would guess. Not what I really wanted to hear as really keen to get on with the HPE especially as time currently tends to be limited.
So I am going to get the car off the lift, give it a good run to check everything else is ok and put it away for now and ignore the problem unless it gets to the point of being unusable.
I would appreciate comments on if it will be a problem using the car and what to look out for if I need to stop using it.
Thanks
Peter