There is no water jacket on a B head unless you have a pair of the weird motorhome heads offf a 413/ 426-3 heavy truck engine. If you are talking about the middle port, that is the exhaust crossover on "normal engines" and the water heated crossover on heavy truck / some motorhomes Those heads are easily identifiable as they have a big water port on the ends of the heads.
Other than special race heads like B2 or whatever they were called here is what does and does not interchange from a low deck (361/ 383/ 400) and a tall deck (413/426/440) and there were a few older (I think) 383's made in tall deck
Cranks are different because stroke and main bearings are larger in tall decks
Intake are different because wider on tall decks
Distributor is a bit longer on tall deck
Pushrods are longer on tall deck
Pans, windage tray, valve covers, timing cover, water pump, rockers, heads, all interchange, and so does the dist. drive gear/ (intermediate shaft) and oil pump, and exhaust manifolds/ headers
I do not remember about alternator brackets, likely different because they tie to the head. Maybe they were drilled for both? Been decades.......................................
I may have forgotten something it's been decades for me