Do you mean HD-HG? Or are you meaning the W sized panel vans ie HQ-WB?

Castle Auto Electrics is worth looking at for info. Here are some kits:

Here is HK-HG: http://www.castleauto.com.au/hs_dbase/efihkgen3.php

HD, HR and HQ-WB: http://www.castleauto.com.au/hs_dbase/efigen3.php

Obviously you don't need all the stuff on these pages, but it gives you an idea of how much it'll cost to "plug and play", ie basically buy the bits and bolt it all in without doing much yourself.

If it was me, and it was a W sized (HQ-WB) van i'd be using a VY LS1 and 4L65E out of a 1-tonner or Crewman (or VZ but this requires a bit more mucking around with the drive by wire throttle). This way you can keep all your factory tunnel and use a TH400 T-bar and make it all appear stock. As you can see on the lists they sell bracket kits to mount a Sanden A/C compressor up high on the LHS if you wish to run factory air. They also have weld rings for your standard tank to fit a VT fuel pump, but i'd be trying to fit a VN-VS fuel tank with swirl pot up high where the standard tank fits. Needs a filler neck mod, but I have a diagram here that will convert the sender signal into the right signal to drive a late HQ-WB fuel guage correctly.