[79 silverado]

That front bumper looks like its molded for the 1981-up Style front end, not the 73-80... If it uses the factory mounting brackets you'll probably need to pick some of those up as well so it sits properly, and it may be kind of tight on the fenders unless you're switching to a 81-up front clip when you do the fenders/hood swap (but you would need to change the inner wheelwells and core support as well...)