Bristow bought the aircraft from the German Army as I recall and did the "T" mod themselves at Redhill.
The 58T used a twin pack concept....two Pratt and Whitney PT-6 engines driving a combining gear box then a drive shaft input to the man transmission.
The twin pac is generally the same as in the Bell 212.
With Dash Six PT-6's the old girl had good single engine power....not as good as the Wessex with two big Gnome's unfortunately.
The Wessex used a different concept to get the drive to the MGB.