I'm assuming its a '69 since you have '69 GMC on your sig line. You can make it look like '68 Chevy without changing your fenders and radiator support, but you have to change the hood, the grill and the bumper. You will have have to drill out the GMC headlight bracket radiator bracket on the radiator support.
If you want it look like a '69 - '72 Chevy, you have to change the whole front clip like Andy said, but you can still use your hood. I feel you on wanting change the grill. I overwhelmingly prefer the Chevy's too. Just tell 'em you're giving your truck LASIK surgery!
