1973 318 - daily driver for years - now won’t start

Instead of just guessing and keep throwing money at it by replacing stuff, I think you should do some testing instead.

If there's fuel entering the engine and spark at the plugs, it could be the spark is too weak or timing is way off.
- How much voltage is at the coil with the ignition ON?
- How much voltage is at the coil with the ignition at the CRANK-position (2-person job)?
- You can temporarily bypass the coil with a wire from battery-POS to Coil-POS terminal. This way the coil gets full battery power and should throw a stronger spark.

- Verify that TDC on the crank still matches with the ignition distributor that the cylinder. 1 (or 6) is (close to) being fired. (If it's really off, the timing chain could have jumped a tooth or more / worn timing chain-set).
- To test for wear, put a socket and wrench on the crank-bolt and rotate it alternating left and right and try to feel if there is a lot of slack.
- - You can also remove the distributor cap and watch the rotor for movement when you rotate the crank left&right. If there's much delay in rotor-movement there's will be a lot of slack in the timing chain.
Severe timing chain-slack or a jumped chain, will also have the engine valve-actions retarded a lot.