How can the connection between a subsystem block and a block external to the subsystem be determined

I need to get the connection between a block external to a subsystem and a block internal to a subsystem. The block external has transformation matrix information and so does the internal block. I need to compare the two automatically and in order.

I have the in order part worked out. Just need to get in order thru the subsystem.

I don't see anything with the internal or external block Handles/Ports/Lines that would tell me they are connect thru the subsystem ports.

Would a mask interfere for the returned Handles/Ports/Lines from the subsystem?