I understand the high miles, when I was going to and from work in my RR it was costing about £90 a week in fuel. After getting a company van I now pay that a month.
But I've seen too many people suffer issues with LPG when fitted to modern cars. Couple in the increased costs of LPG, the costs of a kit*, the servicing costs, the kit on a mates 4.4 V8 costs him £120 a year to service. You're not really saving money.
You'll get some people saying "what about the fire risks"... you're driving a car driven by volatile chemicals, doesn't matter what fuels it, there is always a fire risk. Otherwise it wouldn't move.
Maybe time to learn how to use a lighter right foot? The 2.5 should get ~40MPG anyway. That is loads. ;D
* (make sure it is declared to DVLA, you will save around £50 on VED plus insurance will cover it, otherwise your policy is invalid in the event of a crash)