So I've got this motor number matching to car. It's still got the original ford spark leads and the clock shows 9682 miles. The car came rust free (relatively) with no accident damage just dents from having stuff stored on top so I reckon it's been round the clock once but no more. But it's possible it's done only the 9682 but wishful thinking. Anyway came with no exhaust headers and 4cyl diff to make it roll. Hooked up atlas diff and exhaust etc and she started first go with fuel coming out of boat jerry can. Happy with that but engine had a tick or noisy cylinder. Had to work out which one by pulling spark plugs and found cylinder beneath alternator to be culprit so decided buggered piston or crank bearings so need to overhaul. So pulled motor out today but found when out and pulling off headers that one of the gaskets which was on this piston was only fixed with one bolt and laying sideways. Now I'm convinced noise came from exhaust noise not engine failure but would like your thoughts. At the end of the day one welsh plug is leaking but how far should I go if it's a working motor.

So it came with no headers you say ?   You must have fitted your own headers as you say one gasket not fitted correctly and
you suspect this is the problem ? .........whats done is done..........moving forward >>>>>>>>>>
You'll regret not examining ALL INTERNALS now that uv got engine out.............do it right.
Hopefully you took comp readings and vaccum readings before pulling motor out as this helps diagnosis for any
present or developing problems. Best to remove heads so as to do a proper inspection and bless the engine with new gaskets
AND Oil Seals all around, along with all new BRASS Welch Plugs.
Check and double check torques on EVERY bolt and nut.  Check EVERY clearance spec.in EVERY dept of the engine........ Replace/repair as reqd......... Dont forget Oil Pump and Timing Gear "lash" and tooth condition.
cheers
Bernie

A cracked manifold or exhaust leak near the head can produce a tick noise in certain circumstances.
Removing the plug lead reduces the gas flow in that exhaust port stopping the noise.
I would at least replace the gaskets, seals and welsh plugs before refitting the engine.

The essex makes a rattly noise when you have a dodgy exhaust seal at the head.  Most likely the extractors were re-hung with the exhaust still attached, meaning that by the time they got to the #1 pipe only one bolt hole would line up.
 
Take the whole extractor off and re-hang, the front lower bolt will need wiggling to make it line up.  Use new gaskets and make sure you put them on the right way as the bolt holes are off centre.  Heat up the car and re-tighten.  
 
If the noise remains, set the tappets while engine is WARM or HOT, 010" and 018".  If noise remains start looking at the rocker arm for wear on the tip, wear in the side slot, and that the push rod is straight (roll it over a pane of glass).     

Thanks for the info. Will probably send it off for full recon. Great block deserves it.