4.250 crank factory 340 block
4.25" crank is pretty cool....around 440 cubes with 4.080" bore diameter. I don´t know about the space to the oil pump pickup with such a big stroke - maybe must be moved to the cover of the pump?
If it´s done below 6000 rpm or not depends on the specific setup....with the right cam, intake and cylinder heads i see no problem such a motor making power past 6500 rpm...
Ramcharger is right, application is important to make suggestions.
Michael