? about bb swap in 71

[71Chevystepside]

I am going to put a 454/400 combo in my 71 chevy stepside instead of the 350/350 combo it came with. Something about the look of the big block makes me say wow everytime I see one.

My question is my cab (72 low hump). Will the 454/400 combo go right in without having to modify the floor or will I have to put in a high hump. I am not to the stage of putting the motor in so I cant just try it yet. I am enbarking on the experience here on this board with someone that has already done this type of swap.

Please let me know.
Rich