[ricnor]

My 1997 K2500 454 4x4 Vortec motor has been running on LPG all the time I have had it but there again at over $9 a gallon it's the only way to go.
I have had a few LPG cars now and apart from the time taken to fill up, about twice as long as filling with petrol, I have noticed no disernable difference in performance or economy.
Basically the larger the engine the less you notice the difference but over here we count on 10% reduction in power (if noticed at all) and 10% less economy, that worked out at 1 mile per gallon for me so buying it at nearly half price in comparison to petrol it was always the way to go, however now the difference is only about 30% cheaper but still worth it to me.
The tanks are made from a lot thicker gauge steel than your petrol tanks and in the event of a crash you should be ok, if it's a fire then you would probably need to get away as quickly as you could. I had two tanks under the car one large on on the drivers side and a smaller one on the passenger side, this gave me about 18 gallons of fuel and I still had the petrol tank if I couldn't get LPG anywhere.
All my cars start on petrol and then when you blip the throttle to 2000rpm it automatically switches over to LPG. None of my cars had multi point injection LPG systems (they are better on economy and power) but just the basic systems and they all have fail safe circuits in that if the sensor doesn't get a signal from the engine to say there is a spark then the gas is cut off, stops them from going bang.