'69 Barracuda T56 swap, floor, cross member

How far back is needed for that shifter/hump?
Is it possible to measure from the floor/firewall seam, or maybe I missed that in this thread.

I have a bench seat 4 speed, I know the bench will not work, but it would be nice to know.
No plans to remove the bench, it's actually extremely comfortable, and the kid wants it to remain too.