fourtrack 75 oil pressures



can anyone tell me what oil i should be using in my 1988 fourtrack 2.8 td ive got 10-40 in at the moment but someone suggested i should put synthetic oil in.

my oil pressures also look rather high, ( running at about 50 mph)at cold its 90 psi and idles at 50 psi

and warmed up its 50 psi and idles at 25.

do these sound ok.

can someone also tell me what the rev range is of a 2.8 turbo, ie.. what is max rpm`s ( in my landcruiser i never go above 4000)

i know all this sounds a bit odd, but ive got a daihatsu engine i have just fitted in my seris 3 1970 landrover and dont know jack about the daihatsu engine. except there one work horse of an engine.