If it were me, I would buy a fiberglass GT350 hood for the car. Your car looks like it's in good shape. I would not cut a hole in your stock hood if it's the original hood.
The other thing is that when people attach just the scoop onto a steel hood it always eventually developes spider craps and ends up looking like crap, and if you get an expensive paint job, it's a waste. This is of course just my opinion.
This place is pretty good for fiberglass parts:
MUSTANG 65-66
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1966 Mustang Coupe
Ford Racing 5.0 HO Motor(Crate)/B303 cam/1.7 RR
TFS TW Heads/Edelbrock Perfor RPM/Holley 650 DP
Mallory Dist/MSD Blaster/Holley Electric Fuel Pump
2.5" Exh H pipe/Flowmasters 40's/Dr.Gas Tailpipes
Lakewood T/A Bars/Aluminum Drive Shaft + loop
Auburn 3.55's/SSBC disc's/C-4 wTCI 2800 stall
Fiberglass hood/trunk/bumpers!(100% Sicilian)