Hi SuziQ, you didn't say but I will assume you have foot stomp starter and still not sure if the starter you bought has the correct pinion gear on it for the flywheel, so be careful. Most Stovebolters keep their 6V starter when converting to 12V. As said, a stock 12V starter will not work with a 6V flywheel.
Can you give us the part number and the vendor of the starter so we can check it out for you? If it's cranking the motor OK without noise, maybe you really have a 6V starter.
I will give you the general wiring to get it started.
The foot start type starter has a button on top. The foot pedal mechanism lever pushes on that button and also makes the pinion gear slide into the flywheel gear. For a 12V conversion you need the type of starter button with what is called a "side terminal". So in other words, it will have a big battery stud terminal and a smaller terminal on the side. The original 6V starter will have a starter button with a big battery stud but not the side terminal. In this explanation the button I speak of is not a button on the dash, we just call that big button mounted on top of starter a button. It's a switch mounted on top that has a button.
So to wire it all up.
1. Positive battery cable to starter button stud.
2. Negative battery cable to a motor bolt (starter motor mounting bolt is good). To be clear, there is no negative "terminal" on starter for battery negative cable.
3. Wire from the starter button side terminal to positive terminal on coil. No lamp switch.
4. Wire from battery positive or from the big starter stud....to one side of ballast. This wire should have a alligator clip on it for now so you can remove wire to stop motor.
5. Other side of ballast to positive terminal on coil.
6. Negative terminal on coil to distributor.
7. You end up with two wires on coil positive.
8. Start motor and report back what happens before changing anything.
9. You sort of had it wired correctly to start motor, but would burn out points in time. It should have started however. Which leads me to the part below.
Additional info to consider:
Keep this in mind. We don't know if it's a wiring thing or not but at least if you follow the instructions it will be right.
We don't know any history of this motor. Was it running good on 6V and you just did a few easy conversion 12V modifications or was it taken apart and put back together. If so: Was the distributor removed and put back correctly. Was it timed. Were the valves adjusted and so on.
Also it can be a fuel problem. It sounds like you don't have the gas tank hooked up, that may be a good thing if truck has been sitting. Squirting gas into carb is OK to see if it fires but it won't run more than 2-3 seconds on those fumes. So maybe that all that is wrong, we don't know. Also, you say it has spark. You can have spark while cranking starter but when you release the foot pedal there will be no spark to continue the running of motor if wired wrong. Also, you need to have a 12V coil that says "EXTERNALLY RESISTED" or "EXTERNAL RESISTOR REQUIRED" . Hopefully you have not burnt the points by a miswire. You have spark. Best place to check is take out a plug, attach it's wire, place the threaded part on clean motor metal and crank. Look for a spark jump. Hopefully the spark plug wires are routed from the distributor correctly according to the firing order. The rotor on the distributor rotates clockwise.COIL
]or starter switch with side terminal. We can discuss why the side terminal later. But it is needed. If you don't have a foot stomp start, I can tell you the wiring for a electro-magnetic solenoid.
The parts linked are available at local auto parts stores like O'reillys, etc.