I have used A14 and A15 distributors in A12, and A12 in A14. No problems.

I suggest that first you fix the idling problem. Then disconnect (and plug) the vacuum advance hose and adjust the timing to 7 degrees BTDC.

Will do mate, cheers.

So I got my swapped dizzy to work... and for future reference this is how I did it.

I swapped an A12 dizzy into an A14 motor.

First swap over the adjusting plates on the underside of the dizzy. I found that my A14 dizzy's adjustment plate was a little different to the A12's.

Find TDC of cylinder #1 by looking at the the valves and the timing mark on your pulley.

With the dizzy out of the car put the dizzy cap on (with the rotor in there a well) and mark on the outside body of the dizzy (with a marker or something) the centre of the number 1 contact (where you're going to put the number 1 high tension lead.)

Take off the dizzy cap and turn the rotor so it's pointing at the mark before sliding the dizzy back into the engine block. When you get toward the bottom the rotor is going to want to slide anti-clock wise (in the direction of the firing order) so you want to turn the rotor clock wise about 20 degrees or so. So when the dizzy is fully installed it is as close as possible to the mark you made before.

Put in the adjusting screw but leave it a little loose to fine tune the timing later. Install your spark plugs high tension lead and everything else you've disconnected.

Start the car and set your timing. I use roughly 10 degrees base timing at about 800rpm. Then set your dwell after that.

Worked for me.

Good on ya. That's exactly how I do it.