First i would do a quick compression test on both cylinders and see what the good/bad word is.
The trans takes 1.5L of oil. Everyone has a brand or type they like. I use Belray gear saver 80W, some guys use ATF type f and some other stuff also.
For the rad, just go get some premixed 50/50 prestone stuff from auto zone or napa or any place like that and fill the rad right up, leave the cap off and fire it, rev it a lil bit and top it up if needed, then throw the cap on.
I would change the plugs for sure, hell why not. Grab some BR8ES plugs and throw them in.
The line sounds like the overflow line for the carb, you can put on back on it and run it the same way the other carb is.