Russ,
I wouldn't go thru all that work if your gonna get rid of the truck any way's and it wont make the worth of the truck go up cuz it wasnt a factory BB truck and as you said with fuel prices people will shy away from a BB over a SB.
What you may consider is buying that BB/Trany combo for 500 bux thats a good deal if the pair are not worn out and offer it to the person that buys the truck for an extra 800 bux and tell 'em you can have a BB for it and i'll even load it in the bed fer ya
let them make the call and do the work to install it. and make a quick 300 bux