In those gear boxes I'd say virtually anything that's slippery is fine, so I'd stick with something you already use in other equipment.
I wouldn't go too thick since the boxes do have a tendency to get flooded with water, you may want to drain it for the winter and refill in the spring. But even that may be overkill, those gear boxes can and have survived decades of abuse.
Your biggest concern will be the wheel bearings all around. When they rust up, they can be a real pain in the butt.
If you're going all out and painting - I did a lot of research on mine and what I came up with is this red/white/blue color scheme. Guy Fay's book - I think it's titled something like "1950s farmall tractors" - or something to that effect - has a picture ... think it's page 9 or 10 (I'll stick a link to it on amazon, and you can do the "look inside" thing to see some of the pages without buying the book - which is a painful $150).
That color scheme matched perfectly with the old paint flecks that were left on mine, so it was nice confirmation. I had been in doubt because I'd seen a lot of other old pictures and talked to a lot of people who say they were all red. I think they probably had a lot of different color schemes.
If I were to do anything different with the paint - I wouldn't have gone with the standard IH color paints - I'd have eyeballed it more to that picture and what I saw as left over paint. The modern color codes seem a bit too bright for matching paint from the 40's/50's. Not a big deal though.
I still use the rake on small fields when I have time to go slow - it's a real pleasure to use. It works better than my more modern rake, picking up every single blade of grass. You just can't go too fast, and you can't get too tight in the corners.
Good luck with yours.