So, just seeing what the difference between the two is EXACTLY.

I have an older car that I believe has the original engine (a 1964 model) that detonates really bad. If it's the original engine with NO modifications, could it still detonate on regular fuel? If I upgraded to 93 from 87, and it still detonated, would I need to add a lead additive or just check the timing????

Thanks in advance

It could certainly knock on todays 87. First check the timing, if its correct then you really need to up the octane. Maybe its already too high? (probably not).
Even with 92-93 you might still have to retard the timing a bit.
Is it a 413?

and maybe the engine's all carboned up....

If it is all carboned up.... Any recommendations? Any worthy treatments to aid in reducing carbon, or is it just in need of a rebuild?

One other thing I noticed was a deep bluish grey smoke coming out of the back when I would punch the throttle. Even before detonation I could a lot of smoke.

The traditional methods of removeing carbon without removing heads can work. Get it running, get it hot, SLOWLY dribble water, "Seafoam" or ATF into the carb while modulating throttle. Should see lots of smoke. Test drive.
You really need to evaluate the timing first though.