Ahh, a fellow yinzer. I'm a southerner now, but grew up in Butler, PA. It is easy to miss it this time of year, but after Christmas I'll be perfectly happy without the snow.
The 137 Is basically an updated 136, which itself is an updated 36. Being a clamshell, there is not a ton of easy stuff to do on that saw. Good news is that it is cheap and easily replaceable. If you make a porting boo-boo on it, you're not out much. That saw is pretty much 100% Poulan with orange clothes on. The engine/clutch assy is used in several Poulan models and carries the exact same part number. Since that saw is a wildthing at heart, I would suggest that you read
this thread in it's entirety. Also read as much as you can about porting before you get out the grinder. Do not expect to get anything near the performance these guys get on your first try. Most of the guys in the wildthing thread have tons of experience, and thousands of dollars of ruined cylinders to show for it. Also, you might want to post in the chainsaw section. The builders all hang out over there.