Stop thinking about the timing. If it runs on the choke, it will run off the choke regardless of Timing. Timing is not directly related to mixture.

Your idle speed should be set to what your cam vendor recommends. If it is an unknown vendor, set the timing to 1100 to 1500 RPM -- yes that's high, but the A12 will run fine with it at that setting. You can burrow mom's car and watch the tacho to get a listen for the tone of her engine at 1100 or 1500 RPM. The set your A to the same frequency. Or borrow a $20 rpm gauge.

Once you get the engine running at idle ... then you can set the timing, then afterwards set the final idle-speed and idle-mixture.

To set the timing, there is no need to remove a spark plug -- not if the engine runs with the choke! That's only used to install the distributor. See Timing and stop listening to mates who are not very experienced.