Hello davey,
There are quite a few mw's being restored in yorkshire. It looks a fairly complete truck you have. Have you found the chassis number?
The Z number should be on the doors, i think it was mainly the aeroscreen MW's that had it on the bonnet. It would have been on the back of the rear body below the tailboard, the best chance you have of finding the original z number is to find it on the truck, so be carefull removing the old paint. If your very lucky the RLC museum may have the card for your truck and the z number and contract number will be there, i think it costs £25 to do a search, if you look up the rlc museum on google you will find the details there.
The contarct number was generaly on a small plate on the body, and on a small plate on top of the dash, do you have any original plates for it?
To change the core plugs you need to take the engine out, as there is a core plug on the back of the engine, and if the others are weeping that one needs doing to.
The rear lights shoulf be rubbolites No 5 and 5a one brake light and one rear light, like this,
Best wishes
John