It's the shape of the bridge that largely gives it away as being a Venus 188. The Valjoux 7730/3/4/6 are actually derived from the Venus 188 as Venus went out of business in 1966 and were bought up by Valjoux and the movements are all very similar.

The Venus 188 was a very popular movement in its own right, used by Breitling among others, but during that period Heuer predominantly used Valjoux movements, with the odd Lemania thrown into the mix.