The G&P-made miniturbo head is 41mm wide. The G&P miniturbo reflector is 39mm wide and very deep. Each will fit the other and no other reflector or head. But the setup will fit any Surefire P-compatible body.
The head and lamp assembly were sold by G&P, Digilight USA, LEDWave, Cabellas, and maybe one or two other brands. They are interchangeable.
The most common voltage was 9V (nominal), which works well with two lithium-ions. A 12V version was also made. Maybe a 6V, too. In any event, in all such lamp assemblies the bulb can be unscrewed (and unfocused), so you can mix and match bulbs and reflectors. However, the deep 39mm reflector appears to require a longer filament. Lego was hit-or-miss; "high-pressure" bulbs seemed to have the right length. If a bulb was too short, the lamp would never focus.
I have two such heads that I no longer use. One may be missing the glass, but somewhere I've posted a thread about the exact camera-lens filter size needed to replace it. (I've done so once or twice.) If you can't find a head for sale, I'll sell you a compete head and D39 reflector assembly and two or three 9V bulbs for $30 shipped (PayPal), shipped to Greece.