Sounds like you might have a later-than-1965 timing cover/tab on your car. The '61-'65 timing tab was a separate piece bolted to the driver's/manifold side of the timing cover, and it was marked for 0, 5, and 10 degrees BTDC. Starting in '66 the tab was spot-welded to the passenger/distributor side of the timing cover and some of them have marks for before
and after TDC because the Clean Air Package cars specified ATDC timing settings. If your timing tab is on the distributor side of the engine, the lowermost "10" mark is 10°
BTDC, and the uppermost "10" mark is
ATDC. Try for 5° BTDC as a base timing setting with the engine idling at 700 rpm, the vacuum advance hose disconnected, and the vacuum advance hose nipple on the distributor plugged. You'll need to make sure the mark on the crank pulley is actually aligned with 0° (your central "no mark" mark on the tab) at TDC; the outer ring member of the crank pulley, which has the mark, tends to slip relative to the inner hub member. To check this, stick a straightened-out coathanger wire or similar into the frontmost spark plug hole, and turn the engine by hand (easier with no spark plugs installed) until the wire stops moving upward out of the plug hole. Then check where the mark on the crank pulley is relative to the timing indicator.
You'll also want to check for timing chain stretch. Remove the distributor cap and turn the engine manually with the fan and belt in one direction until you see the distributor rotor begin to move. Then turn it the other direction and watch the rotor; if there's any discernible lag between your moving the engine and the rotor turning, the timing chain is slack and will want replacement. It makes sense at that time to do a super-careful job of getting the camshaft timed precisely to optimise your engine's operation for economy. Details are in multiple threads and you can be pointed at one if your engines appear to need this sort of attention.
Tune-up parts and technique suggestions in
this thread. Carburetor operation and repair manuals and links to training movies and carb repair/modification threads are posted
here for free download.