Hardly an expert but I'll give you my 2 cents. Noise from a trans could be a bearing. I think there must be a trick to testing which, accellerating, decellerating, neutral running and so on. Surely someone here knows. I have used Lucas oil in my trans and find it is quieter but it could be different with yours.
Filling the trans is done from the pipe plug on side of the tranny on the passenger side. Not easy to get at for filling but it can be done. If the trans is bone dry and has not had oil in it you may have to put some in the back where the u-joint lives. The Chevy shop manual is the bible for things like this.
Hope this helps a bit.

1949 Chevy 1/2-Ton
"Sedgewick"
In the Gallery
1989 Caprice