Have you plotted out which combination of stroke length, rod beam width and length that just clears the cam?
Longer stroke and/or beam width = closer, shorter rod C-C adds clearance but shortens the rod ratio.
The 235 cam is directly below the rocker arms and close to the crank; the Gen-3 250 etc. moved the cam away from the crank (pushrods angle back toward the rockers) which adds clearance.
