I live on Route 51 and still ride through the West End. The Route 60/Main Street detour is only 2 or 3 blocks up Steuben and then turning down one block back to Main Street.
When I am in town I ride on Liberty or Penn down to the 31st St Bridge (or 16th) and then follow the trail to the Science Center. From there you can navigate over to the stairwell for the West End Bridge or ride under Route 65 behind Heinz Field then turn left toward the West End Bridge (staying on the road). I got used to riding on the bridge (in the travel lanes) when I commuted from the North Side, so I go over the West End Bridge still to get home from town. Traffic on the bridge is slower and they can see you better than when they are dodging potholes on 51. The view from the bridge is better also.
You can certainly get over Smithfield. I just don’t like the stretch of 51 at the approach to the bridge as it is nascarish with potholes galore. People often express themselves verbally for my entertainment when I ride through this area. I guess it is complicated for some drivers.
But to connect to Noblestown you simply ride on Route 60 out of the West End and then turn left on Route 50 (Noblestown Road). That will bring you down near Noble Manor and then past the back of Foster Plaza before climbing again and dripping down into Carnegie.
That is my route to get to Bridgeville, and the return trip is great riding through the tunnel of trees on Route 60 just before the West End. I love that part.