Complex sentence: Difficulties remained, particularly when a pilot having to bail out of a pusher was liable to be drawn into the propeller which, meant that of all the types concerned, only the relatively conventional Swedish Saab 21 of 1943 went into series production.
Split into simpler sentences: Difficulties remained, particularly that a pilot having to bail out of a pusher was liable to be drawn into the propeller. This meant that of all the types concerned, only the relatively conventional Swedish Saab 21 of 1943 went into series production.