question for you first. was the cobra r hood on a vehicle before or is it new? to remove your stock hood remove the 4 nuts that are on the hinges and the grounding strap thats bolted to the hinge area of the firewall and have someone help you lift it off. now for the other hood if its a new fiberglassed hood you will prolly need to have some body work done to make it fit and look right. when i did my hood i had to file down the sides and make them straight so it would fit between the fenders and not be closer or gapped at spots but mine was pretty much straight on top since its got scoops and not so much surface area. but if you got a used hood just have the friend help you lower it back on and put the nuts back on the new hood and adjust the hood so it shuts properly and fits between the fenders. if its to tight to the fenders just loosen the 4-6 bolts along the inside of the fender and pull out or in which ever is needed and tighten them back down pretty easy. but like i said if its a new hood just drop the car off at a local body shop let them test fit it and make it where it fits and let them do it. if its your d.d. then see if they can fit it one day and let you take the car if thats ok. and you prolly wont beable to use the heat shield on the new hood. hope that helps
most likely a 8mm or 10mm fine thread. if you have some old bolts laying around i would find one that fits and go to lowes or someplace and buy 4 matching bolts. no you dont have to use your heatshield cause most aftermarket hoods dont have the holes for the push pins.