There are no 6.125" rods made in Mopar 2.125" crank pins and .984" wrist pins unless you want to spend several thousand dollars to get a custom set made.
A 6.125" rod will be Chevy dimensions 2.100" crank pins and .927" wrist pins.
.002" of an inch will make absolutely no difference in your build.
As far as building a stroker you'll need at least $3000 to $4000 just for the balanced rotating assembly, and once you build large cubic inches (408") you'll need $$$ heads.