I recently put a 20R in a samurai and I didnt want to use the externally regulated alt. I used an internally regulated alt from a newer 22re , the one with the grey oval plug. The plug has three small wires, white = sense, yellow = charge light, red = keyed hot. The 4th and last wire Is a Large(white I believe) wire that is the main charge wire and is all ready in your truck, that goes to the charge post on your alt. you will also need the alt brackets from a newer 22r/re. With this info and a wiring diagram for your truck you should be able to figure it out.
The gm alt is another option. I almost went that way but decided to keep it simple an Toyota reliable.
Oh and I suck at wiring so take this for what its worth but it worked for me. make sure to test everything with a volt meter as you go.
