Brisbane service & tune-up for dual fuel 80 series

Could anyone suggest a gas mechanic in Brisbane/surrounds who is particularly good at servicing and tuning Landcruiser 80 series with dual fuel?

Mine is a '94 80 series with Impco gas parts installed around 30k-40k ago (a few years ago, I bought the truck this year from a low-mileage driver).

I'm not convinced that I'm getting the best economy: about 25L/100km on gas and about 20L/100km on petrol, on mixed suburban/highway use without heavy loading. The exhaust also smells strongly when running on petrol and I'm not sure if that's normal or a result of the way the motor is tuned.

I'm due for a service and not sure whether to take it back to the original installer (Metropolitan Autogas) or if there's another Impco specialist with a particular bent for the Landcruiser. We're heading off on a road-trip (Brisbane-Dubbo-Jindabyne-Brisbane) in a couple of weeks and I'm keen to get it done before we leave.

Many thanks for any advice!

Dave