i went to install the alternator into my 1200. i also picked up a plug to close off the connection to the voltage regulator. [basically u bridge two of the cables going into the stock 1200 regulator, and leave the rest alone.]
the 200b alternator hits the rear adapter plate instead of fitting in snugly next to it. bolt holes are also different. it doesnt fit by a few mm. looks like ill need to use the 200b adapter plate as well. ?

later on ..
good news the alternator had its guts ripped out and had a 55amp system put in the same shell. so my bosch 45amp is now an ingram 55amp. the alternator is ready to go but doesnt fit.. yet

and then ..
SO i took the alternator to my auto eleccy and we found some information in a bosch brochure he had.

200B / L20B stock alternator has a 100mm space inbetween the front and back lower fastening points.
datsun 1200 stock alternator has an 83mm space.

i then had the 55amp alternator put into yet another casing, this one which had a single removable plate on one end that screws onto the alternator then the alternator plate on the engine. this allowed a good neat fit ~83mm (with some additional washers).

so i put it in the car tonight and it was a very snug fit - the stock fan belt only just fit on around the alternator and the top of the alternator touched the lower water hose, to the point it infact rubbed against the metal water outlet on the A12 engine. i also bridged 2 of the old regulator cables to stop it from being used. now i can take out the old reg as my internally regulated 55amper alternator is working !

now i have enough ampers to power all my incar toys! also the alternator has a whistle sound to it, quite noticeable when driving. constant 13.4v is what the voltometer reads most of the time now - compared to my old one which at times went to 15.1 volt or hung around 14.7v randomly.