Did he buy a helicopter or a plank version? It was used in the Bristol Sycamore and Westland built versions of the S55/Whirlwind. Fixed wing was the Provost TI, Pioneer, Twin Pioneer, Pembroke plus a couple of others.
3,000 Rpm, +8lbs (32" MAP) boost was full chat on the Provost T1 and the Sycamore, having flown both.
There are Provost T1s and a Pembroke still flying so they should have the maintenance paperwork.