Hmmm, ok so putting the carriage sidings in place of the goods shed etc. seems logical...
How's this for a thought:
The preserved line shares the station with current operations; DMU's on the nearest platform, Black 5's on the other...??!!
Then you could have the two lines running in - one for current, one for preserved, maybe fenced off or delineated in some way,
or - would they be ok to share the lines?? It could be a junction of the two...??