(1) there is a second bolt hiding on the bottom of the distributor that you can loosen to move the distributor more
(2) your vibration dampener outer ring may have slipped if it is the original 1965 dampener. This would make the timing mark on the ring no longer correct. You can check this using a piston positive stop tool.
Checking the timing mark is VERY easy. The only special tool you need is a TDC stop tool, such as the one sold HERE
To check your timing mark, remove the #1 spark plug and thread the tool into the hole. By hand, rotate the motor counterclockwise until the motor won't turn anymore (the piston has come into contact with the bottom of the TDC tool). Using whiteout, mark the vibration dampener next to the 0 degree or TDC line on the timing tab. Now rotate the motorclockwise until the mtor stops turning. Mark the vibration dampener again at the TDC mark on the timing tab.
Ideally, the two marks on the vibration dampener should be equidistant from the timing mark cast into the dampener. If the two marks are not equidistant, you need to measure the distance between the two, divide it by two, and make a new mark equally distanced from each whiteout mark which will be your new timing mark.
Alternatively, you can use the timing tab as a ruler and measure how far each whiteout mark is from the cast timing mark and then figure where the timing should be.
(3) have you verified that the distributor rotor is not 180 degrees off? The motor will run with the rotor 180 degrees off, but not very well.
To check this, put the timing mark at TDC, pop the cap off the rotor and make sure the rotor is pointed at the #1 plug tower. Now, pull your valve cover and feel the rocker arms on the #1 cylinder. If the #1 piston is at TDC on the compression stroke (which is where you want it to be when the plug fires) the rocker arms on cylinder #1 should both be loose. If the rocker arms are tight, then you are at TDC on the exhaust stroke and need to spin the rotor 180 degrees.
(4) you are making sure that (a) your firing order is still correct (1-5-3-6-2-4) and (b) that you are clipping the timing gun to the #1 wire, right? Also, if you are using a dial back timing light, make sure it is set to 0. I've made that mistake before.
