Even that would be very impractical.
You'd have to find a .311" barrel blank and have it custom machined including all the proper journal diameters for an RPK gas block, RPK front sight tower, trunnion, RPK handgaurd retainer, and small enough to fit under the handgaurds.
Then have the thing installed and headspaced. It would probably cost more than the gun to have all this done.
And you'd only end up with a barrel slightly heavier than the standard one.
You could make your own gas block and front sight tower if you were a machinist, thus allowing a much heavier barrel.
Trying to turn the PSL into something it isn't is a losing proposition. They CAN be improved, but it's only worth pursuing if you really like the platform and are doing just to see what can be done, rather than setting an unrealistic goal and trying to reach it.
If you just want cheap ammo, the PSL isn't for you anyway. '54R isn't that cheap any more.
For a lot less money you could get a half-dozen Mosin Nagants, pick the most accurate one, than recrown the barrel and bed the action and you'll get much, much better results.