You can use the 3spd but you need a V8 3spd input shaft and cover. The rest is the same.
You can use the diff but you are better off with a V8 Salisbury. With a 3spd you can get away with a 3.08 or a 3.36 as the 3spd has a far more friendly reverse than a 4spd.
Gearbox crossmember is the same.

You also will need:

V8 clutch pedal from a later HZ or WB.
V8 clutch cable.
Bellhousing and fork from V8 3spd or 4spd latte HZ, WB or VC-VK.
Tailshaft from a HQ-WB ute/van/wagon/Statesman that was originally fitted with a 253 (any box) or 308 manual or 308 Trimatic.
Speedo cable gear to suit the diff ratio.
WB V8 radiator and shroud.
WB V8 throttle cable.
V8 accelerator pedal from HJ to WB.

Plus a WB 253 or Trimatic pattern 308. A VC-VK engine will work too but you’ll need a sump/pickup from a HQ-WB plus exhaust manifolds too. Possibly engine mount adapters as well. You could also build up a red 4.2 and fit a 308 intake plus a WB 4.2 carby.

You’ll need a WB V8 engine harness too.

Almost forgot, a HQ to way up into the 90’s V8 flywheel and bush for the crank for an Aussie 3/4spd.

I’ve assumed it’s a ute or van. If it’s a cab-chassis you can re-use the diff and tailshaft but get the diff rebuilt with 3.08 or 3.36 gears as it will be either 3.55 or 4.44 now.

Edited by user Saturday, 20 February 2021 7:43:38 PM(UTC)  | Reason: Not specified