Craig - I just checked through several of my original 1955-59 dealer sales pamphlets and only saw two instances where TF trucks were shown equipped with external cab step. The LCFs all had them and I did see selected "Big Bolt" trucks for 1956 that had them pictured.
Here's a copy of the
1955 Chevrolet Truck Engineering Features book that details the first year TF trucks. Then this
1956 Chevrolet Truck Engineering Features book has pictures of the 2-1/2 ton 10000 Series conventional cab series that shows external cab steps. In reading the '56 book, it indicates that these external running boards for the 10000 Series trucks were also offered as optional on 4000, 6000 and 8000 Series (see screenshot extract below).
I couldn't find a 1957 Chevrolet Truck Engineering Features book to confirm if those continued for '57, but this
1958 Chevrolet Truck Engineering book continues to show the same external steps/running boards on the big truck series. The
1959 Chevrolet Truck Engineering Features book also continues to show the same big truck external steps/running boards too. Although not stated in the '58 or '59 books that I saw, I think we can presume that these steps/running boards continued to be offered as options for the 4000, 6000 and 800 Series trucks, the same as in '56.
