Greg,
I just looked at my 235. I think it is a '58 version. The problematic clamp screw was flip flopped in the clamp and has a small hex head that is real easy to get to.
This engine has the same setup...a bolt clamps through a elongated hole to allow the timing to be adjusted. There are no BTDC/ATCD marks on it as was on the plate for the 'octane selector'.
The octane selector was a merely the timing adjuster (GM gimmick) in drag. I didn't realize a '54 still had this device on it. I think some were adjustable by hand, and I think all had timing marks stamped into the plate...does yours?
When we would time one of these engines, the bolt was loosened and the vacuum advance was a real convenient handle to grab to slightly turn the distributor either way...then the bolt was tightened down.
Stuart
