Windshield Wiper Hole Placement

[Maximus1]

Not sure if anyone is still active on here for A&C but I’ll ask in hopes. I have to have wipers in my state so I need to install them. I’m planning on drilling the wiper holes before I mount the body on the chassis despite the order in the manual. Pretty much because I have better access while standing in the engine Bay Area vs leaning in from the sides. The manual lays out some measurements. The 6.5 and the 12.5” measurements seem straightforward. However, I’m not sure what they want with the 1/2”. Is the measurement forward from the windshield seal. I have read elsewhere that’s it based on the rubber grommet of the mount, not the windshield. I’m nervous about this part. Really want to get the hole location correct…..and the angle. Thanks. If someone has a picture reference of the wipers, I would appreciate that too.