Differences in rocker design. Block tolerence are all over the place. Slight difference in head deck thickness. Rocker pad hieght differences. Stud angle difference from head to head. Lifter body hieght. Spring installed hieght differences.
All these difference will effect Push Rod length. You have gotten the most accurate information you will ever get by powershift46.
I worked two similar customers setups..... one required 6.300" and the other 6.350". What will yours need?..... You will never know until you...... check what your specific setup needs.