Sunbeam stiletto 998cc (imp) gas ring cylinder head (not a gasket) tunable (YES VERY) did you know the Imp engine was down tuned to fit into the road car.
Roots Group used to race the Stiletto range.
Work on them is not hard ?
the twin Webber carburetors and four branch exhaust, turn the cam shaft cog around and gain a lot more power, as for the "over heating" if the radiator was allowed to get road grime (well it is just behind the N/S/R wheel) then it would run hotter and then as the engine is all Aluminium and the two center cylinders have slightly thinner walls there was always a possibility of distortion but the gas ring idea stopped that.
One let down was the "doughnuts" on the drive shafts. the Stiletto was 'decambered and had servo brakes,
Yes I served my apprenticeship on them with the Roots Group.