Well I will stand corrected if I a wrong but to the best of my knowledge the swinging arm bushes have always been brass. The replacement ones definitely are and I see no reason to have made them in cast iron. It certainly looks like you had a job on your hands there but the main thing is you got them out.
You are right about B3 onwards being on needle rollers. One way to tell is that the B1 and B2 have a grease nipple in the swinging arm. It is important that this be re greased when serviced to prevent seizure such as this.
I would recommend you get the broken bush removed from the sleeve and completely clean and recover the it. These are very hard to find. Bushes are still available and I can supply them if you wish, just let me know.