IIRC the shifter for an E-body is farther rearward on the tailshaft than a B. I think in order to have straight shift rods you will have to move some metal around. If you have noodle shift rods you might get away with minor floor pan surgery. I know that the GF5R (same dimensions) in my '66 B-body required floor pan and torsion bar cross-member modification to fit correctly and retain good drive line angles. G Force will rent you a case to use for mock up if you call them up.