Im in USA but when you get a new aftermarket cam one usually needs about .150/.160 thick lash pad to fit in a aftermarket reatainer.since its thicker and needs support so it don't fall out. But its all best guess on a uncut head. If work is don't then all changes.
Now if I remember right Baz said he.or soembodyelse had lash pads that are countersunk on the back like the stock ones that will seat down in the reatainer and don't need new taller reatainers like the ones sold in USA as the lash pads here are flat bottoms thus not sinking in the stock reatainer. Which can fall out.
Now the machinist should have the valve seats and stems so one can use to the same size lash pad or close to it... I have a assortment from .150 to .200 thick so I got it covered if off a little. But one would want a straight edge and go across the valve stems from 1 -8 and be perfect.( not realistic but one can get close.)
now if your adjustable rockarm threaded stem is srewed down all the way this is a sign of a sunken valve seat(usually on a worn exhaust valve) but on yours to center your wipe patern a smaller less thick lash pad might work to then raise the stem up. but one needs to know the correct up/down to get centered.
I think Spannerfodder.com a Aussie Cortina site has adjustments diagram on Pinto motors which is close to the same on what to do.
http://www.spannerfodder.com/images/the ... ratios.gif
just on a side note. I did put a head together and the lash pads I had .150 where to big with a new cam. I had the screwed POST all the way down and couldnt get the wipe pattern correct. I said, **** IT and stuck a regrind cam in and with the back side cut on regrinds I could raise the post up to get my rockerarm lash correct with the lash pad assorment I had. then install that new cam in another head and was fine