Need a little guidance from the gurus

Like others have said the class A style motorhomes tend to have special tail shafts on the transmission. Its actually a brake but either way they are not what you're looking for. Now for as to which way to go (SB vs BB) I'm partial to a BB. But in general you can do a SB for less and if you are DDing it the gas mileage should be better all things being equal. As far as rear ends go what are you calling expensive? I picked up a complete A-body rear for $500. I mean you might be able to do a Dana 60 from a modern Ford pick up and mod it to fit cheaper but I'm not sure how much you would save...especially if time is a concern which it sounds like it is.