1984 ATC 250r???

[440ex. ehhh!!]

so my dad just bought a 84 250r 3wheeler, same he bought brand new in '84, and we're wondering if you can run 75W-140 oil in it. the book says 75W-90.
I couldn't find a category for trikes on here, so im just hoping somebody who has a 400ex also has or had a 250r
Thanks
Josh

[gtt416ex]

ask around in the 250r forums. a bunch of people have trikes that hang around over there