I have had LPG fitted to my 156 2.0 TS.
It was all quite painless until it came to having to pay but the running costs are now much more reasonable. Included is a 2 year/60,000 mile warranty. The conversion is a sequential injection system, with its own ECU and a 60 litre tank. This give about 50 litres of LPG with a range of about 250 miles. The only addition to the dash is a 2cm square control panel.
I did get about 30 mpg with petrol and now its about 25 with LPG which is about right. Cost per litre is only 42 or 43 pence so a fill up from empty is only just over £20. The tank is a round one that fits into the spare wheel well, causes a bit of a bump in the boot but nothing too bad.
Performance. Its the same. If not a bit better but that is difficult to say as I had a fluids and plugs service before the conversion (53,000 miles). I can safely say there is no reduction in performance.
I'm over the moon with it. It was well fitted, they lent me a car for the 5 days it took, the install was good and I'm saving money each mile I drive.
The cost to install was £1550 but as long as there is a 50pence differential between petrol and LPG and I do 12K miles per year it pays for itself in 18 months.
Other benefits, £10 off road fund licence, no congestion charge in London if you register and (this is the main one) apparently free parking in Milton Keynes, beat that.
The near 300 mile round trip to York at the weekend proved all was ok. so the calibration check after 1000 miles is not too far off.
I'll update if I have any problems.