Beside a 1/1000 speed I find often on Fed 1. I was surprises to find a routed slot for a slow speed arm. No other preparations have been made on this camera. The serial number is 136XXX. Everything is original and in untouched condition. Alas I do not own this camera, its just here for cleaning and service.
that's more or less normal on cameras around this serial numbers and later ones. I have seen those holes also on very early Zorki 1. It seems that the top plates were made for the FED with slow speeds that was never build in mass production.
Ulrich is right. It's for that reason that the cover was transformed from "round" to "angular": just to allow the tranmission towards the slow speed dial and spring. Like on the Leica III.