Ahhh the ABLR, have ever used an ABLR or tried to develop a load. That's a whole other black hole discussion. Plus it's impossible to determine what velocities you're going to achieve with a short light barrel and any given bullet, but a PRC will still be faster then a CM from say a 22 inch barrel.
A Defiance XM Anti X + a Proof Sporter stock + a 22in Proof Sendero light might put you in that 5lb ish range.
The following major components would be a good start
Defiance Anti-X XM length 22.8 ounces
Proof Light Weight Mountain Hunter 20ish ounces
Proof Sendero Light 22in .264 45 ounces
85 ounces, a hair over 5lbs. Once the barrel is threaded, chambered, you'll loose a little more weight. If you are building a 6.5 PRC I strongly recommend using a medium length action. It will make life much easier.