Hey Vic. That's my pic above. Link here -->
http://www.zpost.com/forums/showthread.php?t=503948
Yeah, it's a nutty install for sure.
The best advice I got is: position the unit where you want it, then FORCE each self-tapping screw in one at a time. I started with the one on the bottom tang, and then did the one on the bottom left (pictured).
That last empty hold you see there? Yeah, there's a large hole behind it, left from the previous stock scoop. So NO WAY a screw will go there. However, there's enough BEEF that it's not necessary. I would do as the link Dubbedown provided said --> drill new holes.
A VERY long phillips screwdriver is a must as Moustich said. And it doesn't hurt to be a contortionist either.
Oh yeah, and whatever you do, make sure to place a rag or something below you to catch any errant screws. If you lose a screw there and it drops down... you'll have to take the entire under-pan off to get it (or let it rust and rattle down there).
Hope that helps.