On my 66 corvette s.b.I believe it came with AC 44 spark plugs from the factory.
Now that they are not available any more does anyone(know)
the correct replacement ? AC-43,AC-45,AC-46 ? Let me know
what you think before I spend my money...

The AC 43 is a colder plug, AC 45 a hotter plug (used on may Chevy V-8s). Of course AC 46 is even hotter.

Witch would be the correct replacement plug ?

You will need to decide which is best. If the engine starts fine and the current plugs have a light tan color then one step up or down should be okay. If there is any evidence of dark buildup on the electrodes a hotter plug would be better.

Thanks Chipper....

There is no"correct" spark plug for any car. The factory used an "in-between" heat range plug. The correct heat range would depend on youtr driving.....and the factory plug satisfied the majority of drivers. I would go with the 45 unless you do a lot of (80 MPH) high speed driving.
I would also suggest the R or resistor plug for a Corvette. Will prevent ignition noise in the radio. I use R45 plugs in all my cars including the 6 volt ones and have no problems.

After spending a day on the computer and searching many corvette part sites and auto parts stores napa,autozone and O'reillys.It seams that the AC R43 is like Gean said,it's a plug for open driving (witch is what I do ). The AC R45 is more for city stop and go type of driving. I have decided to go with the AC R43 for my type of driving, My closes big town being 80 miles each way. After a 1000 miles or so I'll pull a plug or two and see what's goin on. THANKS FOR YOUR THOUGHS...