This is an interesting question. According to the last DRGW Timetable/Special Instructions No. 4 (1980), there were no bridge restrictions other than speed and a blanket :"locomotives must not be double-headed" was in place for the entire subdivision.
Both DSNG Timetables No's 1 (1981) and 2 (1984) again mention nothing about double-heading or bridge restriction other than speed.
My memory is that we cut off the helper at Rockwood and re-connected beyond the bridge in 1981-82, but there was no special instruction that I recall addressing this. It was my understanding that the separation was more about double-heading downgrade on the Highline than the bridge. This may have been addressed in our train orders.
When I have more time I will review later timetables and my train orders that I saved from that time.
Mike Ramsey