i asked bout a vy front conversion to my vt and this is the answer i got
I'll happily tell you mate. Don't listen to anyone else on these forums that tells you otherwise, they are wrong. I followed parts of their advice only to be disappointed when things didn't fit properly.
You will need:
VY/VZ bumper (prices vary)
VY/VZ guards (prices vary) and guard liners ($40 each from Holden)
VY/VZ side indicators (prices vary) with new short wiring harness if using VZ guards ($60 each from Holden)
VY/VZ bonnet ($500-$600 from Holden, $150 - $300 second hand)
VY/VZ cowl panel parts (3) (cowl panel part 1, $30, cowl panel part 2 (clips over part 1): $18, cowl panel part 3 seal: $10)
VY/VZ Headlights to suit your bumper (prices vary)
VY/VZ front bumper reo bar ($100 from Holden)
VY/VZ front bumper on VT/VX
Firstly, the VT/VX reo bar (the big bar you see when you take off the bumper) is different (slightly thicker and much heavier) to the VY/VZ reo bar. To install a VY/VZ bumper on a VT/VX you need to use the VY/VZ reo bar. The VY/VZ reo bar is also mounted slightly differently onto the chasis. The mount holes are exactly 20mm lower than the VT/VX mount holes. You can see for yourself if you look on a VY/VZ car (with the bumper and reo off), you'll even see the higher VT/VX mounts holes on the chasis rail as Holden never bothered to revise the chasis rails.
So you will need to re-drill the mounts 20mm lower to fit the new VY/VZ reo bar on. Get yourself a good drill as it is very tough to do. Bolt the new reo on and then your VY/VZ bumper will fit.
VY/VZ bonnet vs VT/VX bonnet
You will need: VY/VZ bonnet, VY/VZ washer jets (two, $10.50 each), VY/VZ cowl panel (two pieces, costs about $40 total), VY/VZ cowl panel seal ($10) and VY/VZ bonnet hinges ($18 each).
Just a note, do not use a VY bumper with a VZ bonnet (and vice versa), it won't fit properly. You can also keep your old VT/VX bonnet if you use a VY bumper (as seen in my pictures), there will be a small gap on either side of the VT/VX cowl panel (where the wipers sit) though.
Bonnet is an easy process. Remove VT/VX bonnet with its hinges and rip off the old cowl panel. Install the new bonnet USING the VY/VZ hinges. VT/VX hinges are different and won't fit properly.
Cowl panel is a little tricky to figure how on how to install but think of it like a puzzle. If I could figure it out, anyone can. It all clips together basically anyway.
VY/VZ no longer has washer jets mounted on the bonnet like the VT/VX models. They are now mounted in the cowl panel (they click in). You can even use your existing VT/VX washer hose and cut it to size. You will even have some left over.
Just a quick note, you can use VY guards on a VZ bumper and vice versa (I have VZ guards with my VY Senator front). VY/VZ guards will fit on VT/VX models with small modification. You need to use a hammer and curve each side of your VT/VZ guard reo (shell) very slightly. To see what bit needs curving, stand over your car and try to put on the new guard while looking down inside and you will see the offending piece of metal.
Two things that will annoy you:
1. You will need to buy new VY/VZ guard liners from Holden ($40 each) as the old VT/VX liners will not fit the new bumper. You can leave them off but you'll get a lot of dirt stuck in your wheel wells and door hinges.
2. VZ models use a different side indicator harness. So if you buy VZ guards (fluted or not), your existing side indicator harness will not fit the new VZ indicators. You'll have to cut them off a wreck. New from Holden they are about $60 a side (short harness), I think not. I got them for $20 for a pair from a wreck. For shits and giggles, the same VT/VX part is only $8 a side. Bloody Holden.
Just learnt that VZ projector headlights, although they look they same as VY projector headlights, they won't fit a VY bumper and vice versa...
Make sure the VY/VZ headlights you buy are the correct ones to fit the model your VY/VZ bumper is from. They bolt and plug straight in perfectly however, if you go for projector headlights (VY/VZ HSV, VY/VZ Calais, VZ SS etc), you will need to modify your dip switch wiring (inside the steering wheel column surround, indicator/high beam stalk). I can provide a diagram from LS1 forums if needed. If you don't modify your dip switch wiring (I haven't yet), then when you select high beams, your low beams will turn off.
VY/VZ side skirts will fit your VT/VX without any problems.
^^ Sounds similar to a post and PM I have made.
But that really sums it all up. It is possible but to get the right parts out of Holden can be a pain as well.
I have converted my VX wagon front to a VZ Senator.