I'm not sure Lubo, the 50s isn't the era I'm most familiar with regarding Heuers.

Heuer certainly produced a handful of up/down chronographs in the 30s - if you search for "up down" here, you should turn up some of Jarl's research on these watches, so it's possible they continued this into the 50s too, but the sales information we have for that period is pretty sketchy.

I'm not familiar with the Valjoux 21 either, more used to Heuer having used 22, 23, 71, 72, 92 and the 77xx family. That movement has some family resemblance to the 92 - I can't see if the Valjoux mark is there under the regulator? Of some concern is that some important parts seem to be missing - does the chronograph actually function?