So long as the gear lube is rated GL-5, our axles are not real fussy about the exact viscosity. 70W-80, 80W-90, 75W-90 etc. is fine for the majority of us. Go with a heavier viscosity like 80W-120 or so if you tow a trailer.
If your Dana 35 has a Tracloc LSD, just make sure the back of the gear lube label says something like "Compatible with limited slip differentials" which means it has the friction modifier additive that the Traclock requires. Probably well over 90% of the gear lubes have the additive so if you need it, it won't be hard to find a suitable gear lube.