You can't port from SH3 to 4. Somebody had started to do something for SH4 a number of months ago, but it was never completed.
With patch 1.4 on the horizon, it is possible that somebody could do something with stock files. However traffic is not very realistic with stock so I am not sure if anybody would be interested in modding it.
Then there are some of the larger mods that have modified the campaign files, however these mods are still changing and probably will continue to for the next while, especially with the patch on the horizon.
So no quick answer for you, however eventually something may happen as far as a spysat for SH4.
By the way, welcome to SUBSIM
RDP