Due note mine started missing around 4500 it would rev with a steadily increasing miss and wouldn't go beyond 7200.

By contrast when the dizzy is in good nick the motor will rev to 8600. When the A12 was in the car on occasion it would see 9100 rpms, this was with a stock un-modded matchbox style distributor.

I ran a track day in May and the car developed a very very slight miss toward the end of the day. The vacuum advance pull rod screw was loosening up. This mounts to the plate that acts as the upper bushing, this was enough to cause an issue. My semi solid motor mounts and a constant diet of 5000-8100 rpms comspiires to buzz bits loose. Loctite, safety wire, lock washers and nylock nuts are the order of the day.

Tom