Anyway, Oorah!! When removing the servo we were able to read the number embossed on the cylinder and, nice surprise, an identification plate screwed behind.
I do hope Paul from Powerbrakes will be able to supply replacement or reconditionned!
progress is progress. I really can't answer your question whether the standard servo is good enough, either trial and error or perhaps someone else knows. My MK1 with a P.I. engine has a Mk 2 servo as this is what I had handy.
My Valentine is fitted with full alloy master cylinder noted "master cylinder (later models)" in Haynes workshop manual. Servo unit is remoted as well.