I put the hood scoop from a 69 Mustang on mine  and bolted it on. Left it on for a couple of years but it never "grew on me" like I thought..so I removed it. (that was 3 hoods ago!)
From what I've "heard" the fiberglass bonded on eventually develop cracks. Bolted on with a gasket underneath would be my choice.
6s6

I would go for a bolt-on.  I have seen too many bonded ones that are cracked and coming apart.  Like with any fiberglass part, you expect to have to do some work on the scoop to make it fit well.  Once you get the bolt holes located, stretch some Saran wrap across the area where the scoop will bolt down.  Rough up the bottom of the scoop with some 40 grit and apply a thin layer of bondo on the scoop where it will mate with the hood.  Press the scoop firmly in place until the bondo sets up.  Then remove the scoop (that is where the Saran Wrap comes in) and file off the bondo, leaving the new parting line that perfectly matches your hood's surface.  Then once you paint the scoop, it will perfectly match the hood with a nice, even, barely visible parting line.  To me, the barely visible gap is better to have than cracks later on. 

If you want a true bonded scoop, then go for a glass hood that has the scoop as part of it.  Then you just have to fret with getting the entire hood to look like it actually belongs on the car.  But they do look good once the work has been done!

JamesW wrote:

This is a bolt on hoodscoop from Branda that was done around 6 years ago, possible longer.  To date, it has not cracked.  I drilled and installed it, then the guy who did the stripes used a body panel type adhesive to bond it on.

I just finished using 3M panel bonding adhesive to attach an old fiberglass hood to a metal frame and I can also attest to how strong the bond is.  I can also affirm MS's remark about how much work it is to get a fiberglass hood (at least the one I have) to fit perfectly.  If I had to do it all over, I would have stuck w/ the metal hood and bonded on the scoop w/ panel bonding adhesive like JamesW.
 

I found and ordered a steel gt-350 hood scoop. Should I bond it or weld it?  I'm just a novice welder. Does the bond stay strong forever?

Ernest, does the steel scoop have a flange underneath so it can be plug-welded from the bottom?  Or just a straight edge that butts into the top of the hood?

Even if it has a straight edge, you could weld a steel angle to the inside of the scoop sides that could then be welded from the underside.

Keep in mind if you show the car, the underside of the hood modifications need to look as good as the top.

Sure. Just be sure you have zero air gap between the scoop and hood before you hit the trigger or it will burn through.

MS wrote:

James, how many MILES are on the hood? Might mean more than how many years it sat on the car.
Today's bonding stuff is probably better than that of ten years ago, but hoods do flex alot.
Personally, I think either installation method looks perfectly fine if not on an original Shelby. The worst thing that can happen is you do it over in a few years.

Not a lot...less than 1000 miles in the last 6 years.  Probably average 30 mile outtings at a time.