Cab swap ?s need a quick answer

[old Chevy guy]

I have a 84 chevy cab off a c10 pickup.Truck had 350 motor and turbo 400 trany.I am currently trying to sell it on craigs list and thought it was sold yesterday but today the guy called up to question the floor hump. I'm not all that into these vintage trucks [Im more of a 67-72 kind of guy].so I dont know the ansers.We both thought he could cut out the center section of the floor for his truck but says the high part goes way up on the firewall and is worried about cutting that much out,that it will weaken the integraty of the cab..His truck is an 88 v 3500 4 wheel drive with a 350 and tubo 400 and a 205np transfer case.Im not sure why the floor is so high,when he said it was a high hump I assumed it was a 4 speed.Does anyone know if the moter sits back or higher on this that the floor needs to be so high?What about cutting the floor out of the other truck is that gonna be a problem to do ? Any help appriciated don't wanna lose the sale need the cash! Thanks