Let's assume you check several rockers and all your pushrods are too short. The best way to establish the proper length is to use an adjustable checking pushrod. Crane, Isky, and others offer adjustable pushrods, but the slickest tool is made by Comp Cams. This tool screws apart just like the others, but rather than having to measure the actual length of the pushrod, the Comp Cams tool reads out the length on the side of the pushrod just like a micrometer. Comp sells individual checking pushrods, or you can purchase an entire set intended for those who build many different types of pushrod engines.