[Stellan Bojerud (RIP)]

Austrian made Bofors guns.

Those had sights type Goerz. Other types were Zeiss (shown by Rob Fast above) or Aga-Baltic (Sweden).

The target-calculators were
1) Bofors FC m/35, m36 and m/38 (Sweden)
2) Goerz (Austria and Poland)
3) Juhasz-Gamma (Hungary)

Polish made carriages (British Mk I A) had six wheelbolts instead of five.

But what type of truck is towing the gun?