We had a PB (PA on steroids - 939 cc engine instead of the 847 cc engine that the PA had). It was, in my opinion, the prettiest car MG ever made. Several unique things about them, 1) no speedometer, but he tach was calibrated in RPM, MPH in second, third and top gears. 2) cable operated brakes - impossible to lock up on dry pavement. 3) no water pump or fan - strictly thermo-siphon cooling (surprisingly efficient, we were stuck in heavy, stop and go traffic in Southern California one summer afternoon for several hours and the car never missed a beat). 4) The generator is mounted vertically at the front of the engine (normal for a lot of prewar MGs), driven through a right angle gear attached to the crankshaft and the other end of the armature went through a flex coupling to another right angle gear to the overhead camshaft. 5) besides being right hand drive, forcing one to shift left handed, the shift pattern is a mirror image of the shift pattern in modern cars (like TA onward). 6) No synchromesh in first gear - or any other gear (one soon learned that shifting was as easy without using the clutch as using it, leading to long clutch life as the only time it was used was to get the car started from a dead stop). The P series cars had the Bishop cam steering like in the TC and like the TC, the steering was worn out. Our PB would actually bring the front wheels off the ground when going over railroad crossings at speed and it was anybodies guess which direction the car would dart off when the front wheels came back down. None the less it was a really neat car and a lot of fun to drive, once one learned all the little idiosyncrasies. One of the fun things, since it had the cable operated brakes and a fly off hand brake, all one had to do to release the hand brake was to stomp on the foot break and then release it and the hand brake would release.
Cheers,