Questions about SM465/M20 transmission?

[tiny norseman]

I purchased a SM465 transmission to convert my 89 4x4 from the automatic 700r4 over to a standard. Anyways, I was wondering what oil I need to put in it? I put 80-90w gear oil. Also , it has a lot of gear noise in 1st and 2nd gears, but in 3rd it is quite. Is that a characteristic of these transmissions, or is the bearings bad? I purchased it from a salvage, so there's not telling, it might have some probs. Any advise would be greatly appreciated.

[tiny norseman]

Hey, I was misinformed about the name of my transmission. It is simply a SM465 and not a M20. So, just ignore the /M20 part in my question.

[Tom]

80-90w is correct for the sm465. I remember 1st [the compound low gear] whining the one time I tried it, otherwise its useless so I never touched it. I don't remember much else other then it shifted slow as molasses and blew up. The M20 I swapped in is so much better in every way except the blowing up part, it also has done that to me lol.