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I have a Packard Pacific 54 with the big straight 8 engine
I wonder if their is an additive to add to the gas to raise the octane .
I have engine rattle when i am in the 70 mph range going up hill

It may not be an octane issue. Could be a fuel delivery issue, so you're leaning out.

May need to retard the ignition timing to eliminate the pinging.

Preignition spark knock is a very common ailment with the 1954 359 engine. The only good solution when I had mine back in the 60s was the use of the super premium gasolines like ARCO Purple, Sun 260, etc. These days retarding the spark (and unfortunately giving back some of the nice performance) is your best bet, other than looking for a cylinder head that will get the CR back down to a number compatible with today's gasolines.

Is it pre-ignition or detonation? Pre-ignition occurs when glowing carbon ignites the mixture prior to the spark plug. Detonation is when glowing carbon results in two flame fronts intersecting each other.

When timing is too advanced the knock is caused by the flame front hitting an advancing piston. If there is excessive carbon in the combustion chamber retarding the timing compensates for the advanced flame front caused by the carbon build up.

When the car was new the automotive press pointed out that the 359 with its high compression flathead was subject to carbon buildup.

I added Octane booster and it helped a lot ,but its still there .
This is a rebuilt engine bored over .40
Maybe the high compression ?
The spark was set as spec on the flywheel.

I seem to remember years ago there was a suggestion that using a distributor from an earlier year was tried? Cannot remember the outcome?

I understand that adding another washer to the inside of the vacuum advance can is supposed to help with this. where the vacuum line goes into the vac advance can on the distributor, you can unscrew a lid, and there is a spring that works against the diaphragm.
Right now, the vac advance can is dead on my 359, and I am waiting for a new can to arrive in the mail. When I get it, I will check for knock, and will also try this extra washer there.
(Credit to Ross for this info) -There are articles sometimes about stuff like this in the Cormerant if you are a member.

Put a dwell meter on the coil and raise the RPM. It should be steady. If it changes then the timing is floating around and the distributor needs to be repaired by someone with the old SUN machine who can verify the advance and consistency. I will put up a picture of the machine in action, but I have to go right now.

Thanks...whats a dwell?