Ed,
Yes, NO-OX ID is a good choice: " . . is an electrically conductive grease that keeps metals free from rust and corrosion . . . "
I suggested the felt rings for use as an "insulator" between the battery posts and the battery cover. The Optima battery placed diagonally in the battery box fits snugly/securely under the the battery top retainer (link given in a post above), but the posts are a little close to the edges of that retainer. Put the inexpensive insulators above the retainer on the battery posts as a cheap, and probably unneeded, "insulator".
The 6v battery box size on 47-55st trucks was designed for the very commonly used Group Size 1.
