Welcome to the Stovebolt!
Are you getting this advice from someone who wants to sell you a '73 Chevy pickup? If you get out your tape measure and check carefully you'll find the track width on that '73 is a bit wider than that of a '54 both front and rear. It has been done, but there are some challenges.
The IFS under a '73 Chevy pickup is basically the same design as Chevy used from '63 through '87. In '72 disk brakes became standard, and there are little changes a along the way, but it basically remains the same.
