Are you sure it wasn't released in Germany?
I know you're very precise, but there might be a complication here:
There are two films with titles that could be translated as "Ein Colt in der Hand des Teufels":
* Una Colt in mano al diavolo (1972, Gianfranco Baldanello)
* Una Colt in pugno al diavolo (1967, Sergio Bergonzelli)
'Pugno' means, of course, 'fist', still the second one seems to be the movie we're talking about here
This title 'Pronto Amigo' really seems 'German' to me, just like 'Hallelujah Compañeros' (Arizona Colt)
When you go to the following address, you can watch the international trailer first, then the Italian trailer (click on 'pugno del diavolo', in the right corner); you'll notice the Italian trailer is longer and contains some very violent scenes that were apparently cut from the international trailer (and who knows the international release as well)