I used Volvo anti squeak tape, purchased in a suitable length for front and rear of bonnet via club member who used to advertise in Miscellany. There are also threads on TM.
Two points.
if nails/screws have NOT been used in construction then the cowl tape was stuck on with a 2pack glue similar to araldite but it sets rock hard and is a real b****r to shift - think stanley knife blades and sandpaper, not easy to avoid damage to surrounding bodywork.
the cowl tape marries to the inside of fold around bonnet edge back and front. I found covering this area with high quality electric insulation tape provided a nice smooth surface for the Volvo tape to work with.
It was a tedious job but the result: Totally Squeak Free

for several 000's miles before selling the car.