The previous owner had a replacement distributor fitted in my MGB and I always suspected it was not quite right. Soon after getting the car I replaced it with a 45D4 type 41610 which is the original spec fitted to the car.
I took a closer look at that replacement dizzy recently and quite surprised how different it performs considering it is supposed to be a replacement!!
The max advance on the original is 12deg but there is a total of 20deg advance on the replacement which gives 24/40deg resp. at the crankshaft. Considering the static advance is supposed to be 10deg as the crank the replacement gives an awful lot of advance – 34/50deg resp total advance.
They say you should to be careful if exceeding about 34deg and if you hear any pinking then retard the ingnition until there is no pinking.
So you think you are getting a similar replacement then beware. There are no manuf. markings at all on the dizzy that came with the car so could be any spec (which it is). Would recommend getting an original Lucas to the type that suits your car- there should be markings stamped/cast in to the body of the dizzy – so you know what it is.
Food for thought.