I put 2 at the rear, right next to the raised portion of the hood.
I originally put four down each side, equally spaced. Starting just after the radius at the front of the hood (fasteners only on the flat portion).
The hood fluttered at 55 and made me uncomfortable at 70. Also, being a daily driver, I feared it was too easy to steel my hood. So!!!
I replaced one dzus fastener on each side with one of the locking hood-pin kits from Mr. Gasket. This way you can't remove the hood without first unlocking the pin (no one steals it!).
I then took the two dzus fasteners I removed, and attached them vertically on the grill, so the fasteners are attached on the lip of the hood--I shaved my hood trim/eyebrows so it's not a clearance problem for me.
This got rid of the flutter, and made the hood much more firmly attached to the car. The hood no longer flutters.
A few tips:
Measure a million times, only drill once!
When I drilled the holes for my fasteners, I used (IIRC) a 3/8" bit and an 17/32" drill bit. The 3/8" drills the hole so the fastener can fit through the hood. The 17/32" was using to "countersink" the diameter of the 3/8 hole so the fastener could sit flush with the hood. Remember, the less material you can removed, the stronger the hood is going to be.
When installing the brackets to the car, here is my advice...don't use rivets!
These are the steps I took...
Measure the thickness of the hood, and place the brackets that far below the lines of the car (so the hood fits flush). Pop rivet the bracket in place (temporary) using the two outside holes--this eliminates the need of several pairs of hands while drilling/fitting/etc. Like so:
(My car is the blue '72, the '70 in the b/g is my fathers)
It helps to put a piece of easy-release tap on the fenders where each bracket is placed. Also helps to mark the center of the bracket on the tape.
Place the hood on and test the height of the brackets by visual inspection....mark on the tape which ones need to go up or down.
Here's where I deviate from what most manufacturers recommend...
Instead of using pop rivets to permanantly install the brackets, I used stainless self tapping sheet metal screws.
Using pop rivets I could break the bracket loose with my bare hands--not the case with sheet metal screws--it's much more stable. Plus, if you use a slightly undersize sheet metal screw, you give yourself a bit of adjustability just in case the hood doesn't fit quite right (high/low).
Once the brackets are in place, use steel rivets to attach the springs to the mounting plates. Aluminum would work, but are a little more likely to fatigue and break loose.
Measure, mark, and drill 3/8" holes where each dzus fastener will go on the hood. Test fit to make sure you didn't screw up. Once you're comfortable with it, use the 17/32" bit to countersink the hole so the fastener will fit flush to the hood. DO NOT drill the 1/8" holes for the rivets yet!
Test fit the hood again, this time you can attach it using the Dzus fasteners.
Depending on the parts your ordered (hood thickness, dzus fastener length, spring height) you may have to either sand down the thickness of the hood (LIGHTLY ONLY!) If it's not going to work correctly, you can modify the spring height slightly or order new parts! I had to order slightly shorter springs
Once you get the hood on, and all the dzus fasteners fitting properly, line up everything how you want it and drill the 1/8" holes that fasten the fasteners to the hood. I started the holes at this point, then removed the hood/fasteners and drilled completely through while the hood was on the bench.
Use ALUMINUM pop rivets to attach the fasteners to the hood. Steel ones take more force to set, and could fracture the hood with the added tension. Remember, you don't need a lot of strength here as all these rivets do is keep the fasteners from falling off while the hood is off.
Remember, you don't wan't the dzus fasteners to be *TIGHT* but you do want them to positively rock-over (click) so you know they won't come loose with vibration. Continually check all the mounting hardward, as pop rivets can come loose or shear off fairly easily.