Risky, no (well, no more so than having the rear lights in the boot with the tank) but the real estate between the shock towers will be taken up by the tank.
You can't search for images of VT Commodores that you like and work back from there? If you do find a body mod you like and can't ID who made it I'm sure there will be someone on here who can if you post up a pic. Painting them will always be expensive, so used, in the colour of your car, is the cheapest option. Buy your new VT in a common colour. White?
LPG is great for saving on the cost of fuel (it's about half that of petrol, even considering that you use more of it) but there are LPG conversions and LPG conversions; not all are equally good. I believe the safest approach is to use the factory LPG or one that uses similar components. It's not the only way to go but at least you know that it can be made to work, something not necessarily true of other systems. Look for Impco for a start .
It's probably better, if not necessarily cheaper in the short term, to consider buying a car without LPG and having it converted yourself. That opens up a much wider range of cars to look at and you can then chose what LPG system you have (fitted). Cars on LPG tend to be high km (not necessarily a bad thing per se) and abused. Do carefully note what is included in the conversion. Some installers will do more and some less than others. Cheapest is not always best.