The ones for 55-57 have the neck to the rear. This is to obtain access to the cap, as it would be covered by the GMC cross over piece that provides structure and holds the hood pop spring rest. I used an aftermarket aluminum on my 1956 GMC. The 58 and 59 radiators and the crossover/hood latch is basically the same as Chevy. Jim Carter has a MER830 says it's 55-59, does not name it GMC, but it is. $425. And a MER830A, guessing Alumimum. $445.
