One interesting interview i seen told how an ex beau pilot tried a prototype RR Merlin powered beau. But apparently this ruined the flight characteristics and only one was ever converted but never flown in combat.
Many more than one and almost all of the 600+ were flown in combat - see below. I would think your quoted beau pilot might have flown one of the two Mk V's and the turret was what ruined the flight characteristics given the known horizontal and vertical stability problems the type had as the turret would have aggravated those
From wiki
Beaufighter Mk IIF -- however well the Beaufighter performed, the
Short Stirling bomber programme by late 1941 had a higher priority for the Hercules engine, and the Rolls-Royce Merlin XX-powered Mk IIF night fighter was the result
Beaufighter Mk III/IV -- The Mark III and Mark IV were to be Hercules and Merlin powered Beaufighters with a new, slimmer fuselage, carrying an armament of six cannons and six machine guns that improved performance. The necessary costs of the changes to the production line led to the curtailing of the marks.
[37]
Beaufighter Mk V -- the Vs had a
Boulton Paul turret with four 0.303 in (7.7 mm) machine guns mounted aft of the cockpit supplanting one pair of cannons and the wing-mounted machine guns. Only two (Merlin-engined) Mk Vs were built. When tested by the A&AEE,
R2274 was capable of 302 mph at 19,000 ft.
[38]
Beaufighter Australian experimental classes -- twin Merlin engines; 40mm Bofors gun fitted
According to
Bristol Beaufighter Twin-Engine Heavy Fighter / Night-Fighter Aircraft - United Kingdom Mk IIF - Fitted with Rolls-Royce Merlin XX inline engines developing 1,280 horsepower each; 597 produced.