Think its about 125psi for a 2.0 litre (Turned on the starter motor with a good batt, choke off and accelerator depressed full), which isn't alot. Remember compression ratio is only 6.7...6.9:1 depending if you have a copper or steel head gasget respectively. My dads 2.0 is around 80psi (don't know if the guage is accurate though) and still runs resionably well though I'm sure its not quite doing its rated 52bhp (keeps up with my very good running 2.25D pritty well though!). If its even between pots thats the main thing, rebuild it if its just too underpowered and drinking oil.
If that were mine 'd be tempted to just chuck a new head gasket on it and have another go, see how it goes. If it drives resionable then you can stick the grand+ needed for rebuilding it proper in a high interest acount for a bit longer! These old engines rarely just let go, they just loose more and more power till you find yourself droping too many gears on hills (I'm sure there are lots of landys out there are down on power but run nicely and their owners just think they are all that slow, I did untill I got overtaken going up a hill when unladen by a fully loaded 80in (I know you can't fit much in an 80in but this one had alot in it! Aparently the new camshaft made the big difference). If you do need bits its all avalable from Cox and Turner - he's also good to ring up for advice/chat.