simple

at what point or reason would a longer then stock pushrod need too be used?

sssalah

When a small base circle cam is used or when taller valves are put in, also if a taller deck block is used, but thats not an option for an LT1. In any case if doing significant changes that would affect optimum pushrod length, it is a must to check the vavltrain geometry and rocker to valve contact with a pushrod checking tool. Then order the correct length pushrods.

rskrause

Most common reason is swapping in a bigger (more lift) cam. Sounds bassackwards, but with most high lift cams the base circle radius is smaller rather than the nose being taller. Changing heads can also be a reason, among others.

Rich