I'm in middle of rebuilding a 1998 4.6..I've been a mechanic for over 40 years,buy I haven't ran across this .after tearing the engine down I noticed it has 4 connecting rods of one kind and 4 of another..this engine has never been taken apart..as I didn't mark them when I took them out..I don't know if they were arranged a certain way or what?.has anyone seen or heard of this?.4 are narrow rounded,and machined well,the others are wider,beefier,and rougher cast..I'm posting a couple pics showing the difference..if anyone knows anything, I'd appreciate it..thank you very much

 

The pistons are also different.

No real answer for you, but it is cool to see different stuff.