The diff lock is brilliant. I went with the electric elocker as I am not a big fan of air lockers.
At the time it was about $1300 I think supplied and installed. It has been in 4 years now problem free.
Amazing improvement in traction. Would I do it again..YES...no question.
The wiper mod is on the forum somewhere. Basically I bought a wiper stalk with intermittent function from a SR5 4wd of a similar model year and swapped it out...nothing else required, no wiring mods or extra relays or anything.
As for the tacho...no idea...never looked into it as I have a scangauge which displays rpm