I have two 951 engines sat here and I am currently changing one over from 24v to 12v, both are 24v and both have what I would call the standard non military starter dog.
When I bought the double crank and water pump pulleys, they came with a military ‘guided’ starter dog.
The parts book suggest military style starter dogs but the engines suggest standard type.
Both engines have rebuild plates on them and the engine is being fitted to a 12v GS of 1975 vintage