How to ferry artillery units in Serbia 14?

[ComradeP]

The bridge engineer unit is scheduled to arrive on the 17th,with a 60% chance to appear starting 06:00.

Unless Volcano Man worked some more editor magic into the scenario and it teleports into the map with a pontoon bridge next to it, a pontoon bridge can't be constructed before the 18th due to the 8 turn pontoon delay before bridging checks are made.