Okay, I need to see a picture of a 54 or 55.1 crossmember.
I finally got to looking at the link you posted, and it has some great information that's clearing up some questions.
I knew most of the advance design rear crossmembers were 3 piece (1 long that was riveted to the top flange on the frame and two smaller supports that were riveted to the bottom flange of the frame and to the long piece).
The long piece has the same part number for 47-53, and it's the two smaller supports that are different depending on the truck you get (height of frame rail).
The 1/2 and 3/4 ton trucks share the same smaller supports.
The 1 ton and 4100's share the same supports. This makes since because the frame is identical from what I can tell; however, I did stumble on the heavy duty option for the 4100 which basically turned it into a 6100.
All the 4400's, and 2 tons share the same supports.
So you basically had three sizes depending on the frame rail height of your truck.
'54 has the same breakdown: one for 3100 and 3600, one for 3800 and 4100 (except heavy duty 4100), and one for the rest of the heavy trucks.
So, I'm guessing that the 54-55.1 series crossmembers are either one piece, or the parts people at GM started selling the whole unit with the supports and quit assigning individual part numbers.
This brings me back to my first sentence.
A picture of a stock 54 or 55.1 crossmember would solve this for me if anyone has one handy.
Last edited by whateverpratt; 11/03/2018 4:40 AM.
