D7 4T115 donkey engine parts

Hello all
i am looking for help with some part numbers for the donkey engine on my 1944 D7 4T115. 
Am i correct in saying the donkey engine on the D7 4T and 3T is the same as the D8 and D6 ? the biggest difference being the 7s and 8s have hi low boxes
i dont own a parts manual for the D7 but i do have a D8 8R parts manual, so i was wondering if the part numbers will be the same for things such as head gaskets and other more complex seals?
Also, what oils do people run in the engines, transmission and final drives? 
straight 30W in the engine? 80-90W in the finals and a 30W or 50W in the transmission?
any other advice, tips or help would be much appreciated
regards 
Sam 

for most cat engines delo gold 15w40 is perfect. there is no need to use mono grade oils multi-grades are superior almost every time and no need to change oil for winter use or dilute it either.
you can also use it in the hydraulics.

in the hydraulics i would use textrans tdh it is a universal 75w80 tractor drive line and hydro oil.
i also use it in the trans in my machine. NOTE only if it has a manual trans and clutch. power shift transmissions use a different oil.

the finals i use torquefluid 454 or 434 depending on enviroment temp.

for a proper recommendation contact your chosen oil companies tech advisory service this is usually a toll free number and there advice is free.

if you are a paid up financial member of acmoc you get access to the tech library im fairly positive there would be a copy of the parts, workshop and owner manuals for your machine available to view.

for a hard copy try jensales on ebay you may even be able to get an original. for some later machines try your dealer as cat does have reprints for some models and its worth the ask.