a 58 with 60+ gran miles in less than 4 years? lol I'm shocked it still has the 63 plate. Do the math.
There likely is room, but you'd have to get really really creative as to if you wanna still be able to use the lower tailgate. Then you'd have to decide what to do with the rear bumper if it's all to be hinged. The gas tank is forward of the frame rail that runs under the tail gate. While the '56 fins are 'glass, the '58s are not. However- on this particular car ('58 Packard) there is some 'glass to worry about. That hood and parts of the nose are made of the stuff. But the headlight pods are steel, as are the fins.