I know a few things about them, not a whole lot.
How is it on torque, , and durability?
Torque, HP and economy are basicly the same as the "LA" version. A freind of mine gets 20 MPG's out of his Poly 318 on a regular bassis. He also has the Hwy gears @ 2.94 The engine can go hundreds of thousands of miles so long as you keep the fluids and filters fresh and changed out regularly.
Performance wise, you'll need to go to Racer Brown for a cam shaft. The pattern of the shaft is different on that engine.
Intakes can be found only used. 4bbl. and dualquad intakes are out there in factory flavor or after market aluminum style.
The poly also uses a bunch of "LA" parts as well.
Timing chain and sprokets, oil slinger, valve springs and seals with the best of all.....crank shaft, though the rear flange is different, year dependent, theres some weirdness going on there with it, I'm not to up on it.
But you can add a 4 inch stroke crank to the poly 318.
Pistons can be ordered easy enuff for it. Custom domes will run ya big bucks.
Heads can be done up OK. There not big flowers of sir. A split duration cam should be used with about 8-10 degress of extra duration to help the poor flow.
You can use a modern tranny. (Overdrive!) if you address the possible weird crank flange. The attaching bolt patterns are the same for the tranny to block.
It will also use the "LA" distributor, so if you wish, a MP distrib. can be used or a Mallory, MSD, accel, etc....can go in there.
Headers by tti are the only game in town that I'm aware of and there very expensive, but highly worth it and recomended!