A body/B body housngs length?

I was told today that a b body housing is actually more narrow than an a body housing is this true? If so will it work if i have already done a relocation kit and tubs? And last question what offset do i now have to run. I know its alot of questions at once but i blew a ford 9in apart a few days ago and just bought new wheels and really dont want to buy new ones they are 3 weeks old. Thanks again for the help i just wanna race!