head gasket

I have a 1976 B1600 Mazda Pickup and I put a 2.8 M diesel in it, I am now having two problems, the orgenal rear end is two low and the engine is red lining to do the speed limit, any ideals on the ratio I need for the diesel engine, the seckond problem is I am getting air back through the radiator and loosing water? will this most probily be the head gasket are a cracked head, there is no sings of oil in the water or water in the oil

my friend had the same problem about redlineing his truck it was the tranny he got it fixed and all was good

my friend had the same problem about redlineing his truck it was the tranny he got it fixed and all was good
do you know what ratio he went with to correct the problem