OK. This is not how I ordered in the past. The pushrod company (I can’t remember who I ordered from last. I think it was Hughesengines.) They said just measure overall length. Bottom of the ball to the top of the cup.
As Rat noted above.. there is "effective" and "overall" length. The measurements you see online for the premade pushrods are all in effective length as far as I can tell.
The cup in the measuring tool I used is .158
The shortest set of ball/cup pushrods I could lay hands on were Comp 7821-16. Overall length 7.396 and just too long. I cannot even get the rocker shaft to settle in the saddle with the adjusters all the way up.
I spoke with Eric at Smith Bros yesterday as well. He was the one that told me they are 2~3 weeks out on pushrod orders.
I found a set of Edelbrock pushrods that are 6.900 ball/cup but they are 3/8 diameter... think that might be too big and cause issues with the through holes in the head.