Hi Guys/Gals. In case anyone is interested, I finally sorted my rattly omega out.
Top end strip recondition and rebuild. It turned out that the cambelt was one tooth out on the camshaft sprockets (from the last owner doing the head gasket), and it was running "late" all the time, hence the backing up etc.
ALL the stem seals were shot along with six hyd. lifters being siezed solid. Water pump was on it's last legs too. All replaced, back together with new hd bolts, gasket, belts etc etc etc. New oil/filters and a few long runs to fill the new lifters up with oil... And it seems I have missed one lifter. It either knocks on the one lifter (too low), or horribly sticks too high, and I get one of the valves headbutting a piston. With the rocker cover off they all look identical. Ah well, I'll sort it out. Forgot to take pictures though.
I cleaned the whole car up today with the intention of selling it, but discovered that it really is a nice car when it is immaculately clean, and also discovered that the front seats tilt back!! I never knew that. It's now like driving a shiny barge down the road whilst sitting in an armchair.