After a big faff around with unrequired engine swaps, gas flowed cylinder head and then intermittent non-running on LPG, I can safely say it is now and finally gas flowed and gas powered
The 4-1 splitter/filter inline on the LPG had a faulty internal filter element which was blocking the gas flow under load. That and an LPG regulator with 159,000 miles meant it was impossible to drive under any form of load, would cut to petrol randomly and the top end power was lacking when I could get there!
So, a hefty bill later, and today I filled up the LPG tank fully for the first time in about 4 months Bye bye 117.9p a litre, hello again to 61.9p a litre
If possible I'd like to get the car on a RR before if nothing else but may not get the time...