The section of the Ma & Pa that might be able to be seen from the Lt Rail station on North Ave is right along Falls Rd. It is already a trail, the Jones Falls Trail. The Ma&Pa RoW climbs out of the valley through the recycling center & the Potts & Callahan facility to cross under 29th & Sisson Sts. The realignment for the trail would be to use the existing "switchback" that comes off the Jones Falls Trail by the Steiff building, so the trail that I'm proposing would have its southern terminous at the Steiff building.
You asked about the North Central RoW: I'm not sure, but I thought that the Lt Rail uses it, which of course is the other side (west) of the valley.
BTW: There is a 1/2 Round house that is visable along the RoW that the city uses to store salt. It was a Ma & Pa facility. I'm not sure how rare a 1/2 round house is. Does anyone know?