One thing I might be able to add re:40y start tech. and this was from Charlie in person.
He said he saw no advantage in holding the back hand/arm up extremely high as you see with some athletes.
He recommended holding the arm up about hip high or possibly a little lower but not so high to the point where it is well above the back hip.
I think he said something about that (hand/arm held very high) being too long of an action to initiate a start and that the lead arm did not need to cover that much distance to get one started.