| One thing on the turbo engine is the fuel rail operates at a very high pressure compared with the normally aspirated versions, hence the slight diesel-like ticking noise the turbo S engine can give.
In principle there shouldn't be any problem to convert a turbo engine to LPG. In fact it can even be better due to the high octane number of LPG, preventing engine knock when running higher boost levels. In practice though, I'm not sure how the LPG would affect various conponents of the engine such as valves etc...
Worth checking to see what kind of warranty the company carrying out the conversion will give, and whether or not it covers damage to the engine. | 
