Im sure it's on here a hundred times but i cant find it and would like to know?

I have just bought a 91 diesel that only has 1/3 oil pressure! Not sure of Ks...
It has a wire dipstick with only a tiny bit for reading on the bottom,an inch or so! and mine is an inch above that reading! is this the genuine dipstick?(a wire one with an inch of reading) if so mine has way to much oil in it and i cant find any pics on google?(very concerning)
I have bought new filters and will do a change next week(the cars not being driven yet)How much oil in one of these pls as i have read 10,11,12 ect?
Best and cheapest oil pls?
I want to run a cup of diesel in it for half hour on idle before draining,would you advise this? i want to try and clean the galleries and figure the shop bought cleaner isnt much different?
As i said it only gets one third oil pressure(Eeeek) but has plenty of grunt(on the two hour drive home) It didnt blow smoke but has been run on idle for a couple of hours while i fix some gremlins in the electrics and does blow some black smoke now under revvs and i figure a good burst when i rego it will cure that(fungers crossed)