Pushrod length should be taken into consideration any time you change your valve train geometry. Incorrect lengths can cause serious damage to other components in the valve train.
Checking for the proper length is a relatively simple task and there are instructional videos on Scorpion TV, Summit Racing, JEGS, and YouTube. Start by purchasing a good Pushrod Length Checking Tool. Always Check and while you are checking for that length, check for pushrod to cylinder head clearance on all ratios. Aftermarket valve covers may be required or valve cover clearance may need to be increased.
Just a few quick checks now can save hours in the end.