Hi
Well will chime in with my thoughts .
Yep have toyota hi lux , mid 80's , diffs in my 413 . Some pic's in my album about the build , very back yard and no cert

.
"Good idea , Bad idea " . All depends on what you are doing ? Standard engine , nope don't do it . You will not have the grunt to turn the tyres you need to get the clearance back with the bigger diff heads . Ran 31's on my zuk axles for over 5 years with lockers and had no worries , until I tryied to pull someone out backwards and spat out a front cv . I knew better and paid the price . You would need 33's atleast to get the same clearance with toy diffs .I have 32x9.5 simex on 6 inch rims so they are tall .
Engine change planned , well then swap them out but pick your engines . The cheap option is not always the best option .
the lux diffs are not lined up for the zuk t/case , better bet is prado diffs , diff heads are offset the good ones are rear disc and already for coils

, just have to be lucky and find them at the right price .
Other diffs I would look at are rangie diffs , lighter than toyota's and wider and a standard zuk engine will never break them , disc and coils allround . Draw back is crap ratio's .
All depends on what you want to do and do you want to do it to a 413 . If you are only planning to change the diffs etc , get a vitara and change the diffs . They are 1.6 , have powersteering . Much more room for bigger engines down the track to match the diffs and the rear is matched to the toyota , ie centered diff .
Oh and definatly coil it while you do it , very

. My diff install was a little harder than most as I have a nissan gearbox , front output is on the left hand side . So i cut the diff in half and moved the head over . Also the front diff head will want to hit the front of the chassis thus limiting up travel compared to the 413 diff that fits insid ethe rail and making a spring purch for leaves will be hard ( not impossible thou ) , all the more reason for coils .
Chris