The oil injection cable will need to be replaced.
Yes, you are missing a suspension bolt, grade 8 is a good idea.
I wouldn't worry about the grooves in the outer case of the clutch, but the face of the sheaves where the belt rides needs to be cleaned up. I use a scotch brite pad when they look that bad. It also appears as though the clutch is stuck. I would disassemble it, and give it a good cleaning removing all the rust and corrosion. Make sure that everything moves freely, then reassemble (do NOT use any kind of lubricant in the clutches).
On a 79' the speedo cable connects to the drive axle on the clutch side, just below the secondary clutch. I have seen many of the flanges that the cable/adapter attaches to break...
I use permatex 51813 on the crankcase, this is what Image Enterprises uses on crankcases. I purchased a tube from them years ago, and have used it on several crankcases without an issue. However, as Jim said earlier, any good sealant that is rated for gas immersion will work.