Last measurement should tell the story - measure from the top of the bellhousing to a given location on the firewall. Or using a straightedge - top of bell to the top of the inner apron tops.
Or top of extension housing to the cross member support horseshoe - the part weld in the car.
Maybe some one here can provide those measurements.
I just put a 383 and 727 in my project 1970 Charger.