LPG

It could be. I've heard of a mob in WA who sell the appropriate kits, but essentially it's remove the old system and install the new one, minus the tank.

I have two vehicles on LPG, a V8 Statesman using the same system as yours and a Pajero with an injected system. The Pajero's system is much better than the Statesman's but no way is it that much better to justify upgrading the Statesman.
I'd only consider changing if I was having trouble with the standard system. eg Pajero's don't run well on the older system, they tend to suffer catastrophic backfires which destroy the airbox and MAF. I've only ever had one minor backfire in the Statesman.

If I was doing it now (installing on the Statesman) I'd definitely go Injected.

Ray,
As the previous response said, top end power, is the only improvement you may get.
For simplicitys sake the throttle fed system you have is adequate. I have the same as you for 10 years now and have never had an issue with it. You may get slightly better economy with an injected system but it recovering the cost will take a very long time.

Rob

Hi Ray
I enquired about this last week to fit Impco injected lpg. They need an oxygen sensor.
If your 80 series is pre 95 it will be ok to fit as they have the oxygen sensor.
95 onwards 80 series the air flow meter was changed and the oxygen sensor removed.
The 100 series with the V8 is ok.
Roughly about 4.5k to fit less the lpg tank and pieces all ready fitted. and less the rebate .

Rob.

Don't waste your money.