So i found couple vehicles(Ford,Bus) with machineguns but it seems you cant aim down iron sights and there is no crosshair so you could know where you aiming, if you could fix this that would be cool, if its possible ofc.

try 0 on your numpad, had the same issue, num 0 helped me

From my experience there has to be a driver in the vehicle, and the engine running, before you can use the iron site.
Would be awesome if we could use it without this constraint but this might be an ARMA II engine issue.

0 on num pad

the ford doesnt work afaik.

it worked for me. thanks for this tip. still something to learn after 2 years origins

Yea, confirmed.. it does not work on the ford transit