The magazine disconnect is a safety feature that is still made in modern firearms like the S*W M&P9 for Police and Military use, as the pistol can be rendered safe quickly by dropping the magazine. Some police departments absolutely require that for their duty issue pistols. I'm not a fan of it for range shooting, as it just makes it hard to drop the hammer after showing clear.
They also didn't all have that spring, since the tactical doctrine of the day for some was to retain the magazine empty or not (hard to reload your magazine from your rucksack if you'd lost all your magazines etc). Shooting on the clock is definitely not as well served by the magazine not falling clear, but if you are looking for the old time set up and not a competition shooter this might work.
Thanks
Colin D