X2: a minimum safe distance for the ring package is step #1, rod length is whatever you have left.
Don't try to use the same CD as another engine, the spaces needed differ quite a bit:
1. actual ring thicknesses (1mm vs. 1/16" etc.).
2. crown down-distance for ring #1 (must be greater if nitrous or blown).
3. minimum crown thickness to prevent valve relief from getting too thin at the bottom. This varies with valve size, placement, stem angle and lift.
4. how long is the skirt? If you have 2" of skirt below the pin (assuming it clears the CW and doesn't hang out of the bore 30° B/A BDC), the CD can be even shorter.

Almost any 1.400" is safe. At 1.300", some. At 1.250" you want a .927" (SBC) pin etc. Below that it's not going to last very long.