Yes, also CMU likes to show the map with North facing down! It took me quite a few minutes to find that out when I saw Forbes Avenue above Fifth Avenue!
BTW, I am the author/creator of the map (http://www.publictransitguide.info/Home/) that @StuInMcCandless and @ejwme have referred to. I grew up in the Coxcomb Hill area and nearly every stretch of pavement (that existed in the 1990's) was touched by my two wheels or two feet. I can help you plan a trip from anywhere in Plum depending on the ride specifications you want (such as challenging hills, fast downhills, slightly rolling, etc.) and based on your level of comfort with other vehicles.
Bus routes that touch or go reasonably* near Plum:
1 - Does not enter Plum, but has fairly good service 7 days per week. You can pick it up at Central City Plaza in New Kensington and at Freeport Road/Hulton Bridge in Harmar (across the river from Oakmont).
67/P67 - 67 Goes within 1/4 mile of Plum at the CCAC Boyce Campus on Weekdays. 67 Operates from Downtown to Monroeville Mall 7 days per week. P67 is the express route from the Mall to Downtown and operates on peak periods only in the peak direction.
68/P68 - If you ride to Monroeville Mall, you can take either route to Downtown (68 requires transfer at Wilkinsburg Busway Station)
77 - Weekdays along Unity-Center Road and CCAC Boyce/ 7 days per week from Alcoma Apartments in Penn Hills to Downtown.
78/P78 - Does not enter Plum, but serves Oakmont on weekdays. P78 goes to Downtown Pittsburgh during peak periods and 78 only goes as far as Wilkinsburg Busway Station for transfer to a P1 to complete trip to downtown.
P12 - Rush hour only service Holiday Park Area on Route 286. This route has reverse commute trips.
P16 - Rush hour only service along Unity-Center Road and near Plum along Hulton Road in Penn Hills. Also serves the intersection of Coxcomb Hill/Hulton Road in East Oakmont (does not go past Golf Course or Ramparts). It only operates in the peak direction.
*My definition of reasonable may not agree with everyone, but I took the rule of approximately 3 miles away from the border of Plum to determine if the route is worth mentioning due to using a bicycle and to show some routes that operate 7 days per week.
Feel free to message me here or get me on twitter, also at @TransitGuru.