Known, I think, as the 'Flatiron', The Thomas Special was built - indeed I believe there were two - for the British GP at Brooklands in...1926 I think.
Engine was 1.5 litres supercharged straight eight, sohc with dry sump lubrication. Pretty advanced for the day. I believe neither car started the race due to pre-event problems and further development was halted by Parry-Thomas' death at Pendine Sands in 1927.