I like to keep the stroke at 3.750 to 3.850 on these blocks for a better rod length and piston design. You can do the 4.125 bore with these strokes and get 400 to 410C.I. combinations. You can do the 4.00 stroke and use a 6.200 rod but you will have a 1.100 compression distance on the piston. This will work fine but will have the pin into the
oil ring and not very good package for boost or nos. If you are running naturally aspirated it would be fine. Just let us know how we can help. Thanks, Keith Craft