I might suggest driving the car for a while with the straight 8. I have one in my 1940 Packard 120 and it has more torque than any of my other cars. It will cruise at 70 all day. I have not had any problems with mine and have been able to find misc. parts at NAPA. I have knee shocks on mine that are expensive to rebuild but ride very nicely. Yours probably doesn't but the ride should still be nice.
You are on the right track with doing the exterior and interior first and driving it for a while. You might actually get the bug to restore it rather than rod it. I personally get more pleasure knowing that it is back to the way it was 48 years ago than to have something that can be easily done by most good rod shops. Driving an old car is like driving a piece of history. Think of the things that happened back in 54 and it almost takes you back as you sit behind the wheel.
I have nothing against rod and like them for what they are but how many people own a Packard? An an original Packard at that!!!!!