Snakebit. I am in the same decision mode 331 vs 347 stroker. The issue you are referring to is the 'wrist pin hole' on the piston used for the 347 is very close to the bottom piston ring. Some say this results in 'a potential' for the motor to burn
oil and, or to cause premature ring wear. Those holding that view therefore favor the 331 as the wrist pin hole is slightly further away from the ring. Joe Sherman of Joe Sherman Racing in Santa Ana, Ca., (apparently well known in the Mustang racer set) says "it's all crap, they cost the same to build, and the 347 has more power". TandL Engines said "we have never built a 331 and we have built literally hundreds of 347's without a problem". I am also trying to find someone who has personal experience with Tand L as they offer a very attractive 347 using Dart Pro I heads, Mahle pistons, Holley carb, and Edelbrock RPM air gap intake. RD