Jon, had to go to the spares shed to take a picture of mag starting handle stuff, so dug out what I have on the shelf.
This is the 1st type of coil nosecone, with the hex bush, and the angled dog type handle shaft 1A 264
Depends where you want to measure from, I have the casting flat on the shelf here wit the steel cam oil thrower thing overhanging. I made it 6 3/4 over the ali part. A smidge under 7 with the brass nut. My Oct '28 AD chummy has one of these. The April '30 AE chummy I sold recently also had one of these. Both fitted the cowl perfectly. My assumption therefore is that these are appropriate for the medium sized (plated) cowl cars, though I have no experience of the saloons of this era.
Couldn't get a dim for the one on the car (RL), and I don't have a spare to measure, but I'd happily pin the one on the car as a 1A459 on the basis I know its the longer version.
So perhaps we could say the long version was for the taller radiator, 3 speed cars?, Not just 'RN' as Daves notation. My assumption again. Any comments?.
I do have a few later short 1A559 on the shelf
My measurement for one of these is 6 1/4 over the ali. I measured 2.
.
So I suggest:
August 1928 - June 1930 (med sized plated cowl) - 1A 264 (6 3/4 long)
June 1930 - October 1932 (tall plated cowl - 3 speed) - 1A 459 (7 1/4 long - Tonys Dimension - 7 1/2 - Jons Dimention. I believe they are more likely to be 7 1/2 on the basis the 4 speed box is 3/4inch longer than a 3 speed box)
October 32 - 1936 (tall plated cowl - 4 speed) - 1A 559 (6 1/4 long)
any more variations?
For shits and giggles here is a 1A 246 (nut style) and a 1A 559 (late type) together. I dare say you could fit the early one to a late car at a push, or vice versa.
Clearly only applies if you put the cowl and engine where Austin intended. Ulster rep and Special builders, none of this need apply to you. Fit your cowl where your nosecone wants it to go. Or at least fit it where you can get a nosecone that fits, or do without a handle.