The spare starter dog bolt I have is from a Commer but I'm almost certain it's the same crank. The measurement across the flats is (as near as damn it) 1 1/4"
or just over 32mm
The thread on the bolt has an outside diameter of 3/4" but if your crank has been drilled out and helicoiled then obviously it will be different in the crank. Are you thinking of getting a new bolt made up to match the thread in the crank of will you be fitting a new helicoil?
Does anyone know the size of the Crankshaft front end nut (Starter Jaws Nut for engaging Starter Handle). I have discovered that mine has a stripped thread and was refitted in the past using a Helicoil insert, which has now come adrift. I therefore need to purchase a nut of the correct size and thread, no need for the Starter Jaws aspect, as oil cooler under the radiator blocks the access anyway.