some people claim that the 55-57 style bird was the only style used on all GMC Task Force trucks,
but no, no, no! This hood bird below was designed only to be used on the 55, 56, & 57 then GMC changed the design in 1958 for the 58 and 59 trucks. There's just not enough literature out there showing this, but if you look real close you can clearly see this in the original GMC advertisements. the Master Parts book for 58 and 59 used old stock photos from 55-57, so that creates a lot of confusion also. Makes for a good debate !
Take a look...

GMC used the 58-59 hood birds up to at least 1962.

Ok now below are a few pic of the 2nd hood ornament that GMC used for their 58 and 59 trucks.

GMC used two different style hood ornaments, 55 to 57 was one and the 58 to 59 was the other style. Here's two pics of the 55-57 bird below,

Do you see the difference? Look at the lines on the front edge of the wings and the noses are different.