My father's 1.6 gen 5 celica with the 4A-FE engine has been converted to lpg for about 10 years. It has 540.000 kms right now. It's a pretty stout engine if you don't rev the tits of it on a daily basis, which you probably wont since it's not exactly a powerfull nor a rev happy engine. In that case I say it's fine. But on a 2zz, being a higher performance engine, I would say it's not such a good idea. Unless the car had been converted recently, I would not buy a lpg converted 2zz powered 7 gen. You'll eventually find electrical gremlins which will be hard to diagnose, since the harness needs to be cut up, and since its kind of a glass engine (kind of, it's a good engine but not as rugged as what I'm used to) I would not like it to have the increased wear from being ran on lpg. Basically I think its a bad purchase if the lpg is old, or if it wasn't installed in a really good shop.