It's best to install it with the windshield out. 3 self tapping screws from the top is the way to go. But, when I installed it initially, I used one self tapping screw on the passenger side, and one rubber hose clamp connected to the roll cage on the drivers side. That held up nicely for a full season. I can provide pics if you'd like.
Just drill holes for your gauges, set it where the regular dash would go with the window out, drill 3 self tapping screws and you're done. A clean, lightweight, custom dash.
PS... I sent you a PM on the NASAForums site.
I tried answering your pm on the NASA board but my newbie status keeps me from sending you something.