Pushrod length can vary if the heads have been milled at some point in their life, or if the block has been decked. This is why I would measure for pushrod length and then order. Head gasket thickness is also a factor.
For example. for the TFS170's I've often heard the ideal pushrod is 6.700-6.750". However, when I measured multiple times, I got a much better pattern, and closer to 90* to the valve at mid-lift with a set of 6.800" pushrods. So that's what I ordered.