Push Rod Length Tool- 360LA

I'll be getting the block back from the shop this week. 72 360, stock crank n rods, KB107's, stock heads, new valve job, heads mildly ported, block n heads were not cut. I'll be installing Com Cam Pro Mag Rockers and Comp Cams XE268 hyd flat tappet cam. I'll need ball to ball end push rods.

Since the heads and block were not cut and I know I'll need to check the push rod length, I was wondering what push rod length tool I'll need. The push rods I removed from the stock block measured 7.5". I've been reading that if the heads n block were not cut and switching to roller tip rockers, the length of the rods will be shorter. True?