Any other ways to increase the horsepower/ torque of a classic car?

1965 ford thunderbird I've been asking around and so far I have. 1 Headers 2 High flow mufflers and pipes 3 H pipes 4 aftermarket pulleys 5 aftermarket fuel pump 6 HEI

The pulleys were a waste of time and money and may hurt drivability, but the other items you list should overall provide a slight increase in power. Of course, as usual, you completely FAIL to provide critical information such as the engine SIZE, but the only way you're going to get noticably more power is from increasing compression or displacement, or both. Again, without the needed information, it's not possible to even say if pistons, cams, heads, or a performance intake are available for your car.

Change out for a different degree camshaft.

If it is a two barrel carb, change the intake manifold and make it 4 barrel if it is 4 barrel upgrade. You can also install electronic ignition. Oh yea always use premium gasoline not regular