A tight distributor makes a huge difference.
I had also a lose dizzy for years with the timing marks not steady under a timing light.
The vacuum advance started to act too soon and too fast right after coming off idle and I never could time the engine right across the rpm range.
Last year the timing started to retard or advance by itself at times.
I replaced the old lose fitting dizzy with a remanufactured one which was very tight and much harder to get inside the block.
Day and night - now the engine sounds better, the timing marks are steady in the light and I could finally get the timing perfectly lean across the rpm range.
The vacuum advance now only kicks in after 1500-2000 rpm and much more slower.
I heard there are different distributors for the early and later blocks, because of the difference in camshaft metals over the years.
Typically parts suppliers don't know and would sell one to go for any year.
Bottom line, if your distributor is too lose, the timing marks move around and the vacuum advance is too snappy and moves too quickly, replace it.
