I havent done this before but i see u have no response from people so figured id chime in. But i have done a manual conversion.
Its definately possible, u will need an engine crane, jacks and stands, socket set etc lots of extension bits to undo the bellhousing from the engine (ive heard its possible to remove an engine with the box still attached)
Anyway so start by disconnecting the loom which should start under ur radiator resovoir, and run through the firewall into the passenger footwell, along the top of the engine and also down behind the engine and along the box. If ur a noobie it sounds daunting but i suggest diving into the deep end because its the best way to learn...
I would also suggest stripping the motor of all hoses and fluids so its in one piece. The motor should have somewhere u can connect some clips and a chain to the crane... once the box is out (if thats the way u wanna go) and the loom is out and all hoses are off all u gotta do is undo the engine mounts from the motor and lift it out...
Now, when putting the new motor in, u will probably need a new subframe, (this is the solid piece that ur engine was connected to... its held on to the chassis by 4 huge bolts... just have a geez ull find them) im not 100 percent sure but u should be able to use the one from the ute if those 4 huge bolts line up on the vt
The 5.7 will fit. Probably best to get an exhaust guy to fix up ur exhaust once ur done.
Other things i would suggest doing to keep the rest of the car on par with the engine would be as follows
- bigger/better brakes
- coilovers
- a new diff (look into that im pretty sure v6 diffs are shitty)
- u should be able to use the gearbox diff and tailshaft from the vz if its all straight...
- and also some good tyres maybe some wider wheels
U should also be able to use the loom and cpu from the ute but ull have to go somewhere and get them to flash ur cpu with manual programming and link your key so ur car doesnt think its being stolen...
Anyway dude like i said i havent done it before but it i reckon i could do it.
Ps itll take u a while so make sure u have a good set up with plenty of space and get the car on all four stands...
Good luck man
(Ps i cant sleep for **** lol)