The FAM would be wrong as it normally is when improvements are made to the design. You just don't know when GM decided to change something that was wrong and improved a design. You can almost count on the FAM to be correct, but there are many areas where it's just flat out wrong. Bed changes, Cab changes, etc etc. I am not a FAN of the FAM for 1954 where they flat out LIED and called it a 47-54 FAM when all drawings are 53 and 54. In researching this problem further, I have heard of a fire that claimed all of the original drawings, laziness, you name it. In the end, anyone who wants accuracy for their 47-53 is just SOL.
Kevin... the problem with plumb bobs, liquid levels, etc is when you use more than one of them so you can get to a different plane is you can lose or gain an unacceptable difference. You cannot have a 1/16th inch problem when trying to bolt up the running boards directly to the rear fenders. They either bolt right up, or they don't. The running board brackets (frame) have their original holes. The running boards mounting brackets are not even close. The first one on one side is over an inch off from the first one on the other side.
It's not a hard question, but I can see it being VERY hard to correct with no sheet metal on the frame. I am looking for added intelligence in that regard...
1) Would you say that the most critical issue is the rear fenders bolting right up to the end?
2) How without sheet metal on the truck can you guarantee that junction is accurate? If there was a measurement that says.. go two inches from the front of the running board and that is where the FRONT hole would be, then since the frame is angled, 2.15 (example) for the second hole, then life would be simpler.
The 1954 frame is not EVEN the same as the 1947. The hump for the bed is lower, the trans crossmember is different. There are many other examples. Shock mounts, the list goes on and on. I THINK the issue at hand is the same so I concur with using it.
I am thinking the best idea is to just wait until the cab is on, the bed is on and the rear fenders are on, then place the running boards on and mark them for the mount brackets. I was just hoping someone knew something I do not about how to place them so I do not have to wait. But I can wait if that's what is recommended. It's not like I know everything, just enough to know you don't just start welding mounting brackets on, or bend the frame brackets to suit the whims of whoever welded them on wrong. I do not have laser measuring equipment and I don't think they did in 1950, so naturally, I was hoping someone knew from experience, bracket ONE.. goes xx inches from the front. bracket TWO.. goes XX inches from the front. bracket three goes XX inched from the front. Then, there is XX inches between bracket 1 and 3, 1 and 2, and 2 and 3 to confirm ABSOLUTELY before painting and refinishing these running boards.
Once those measurements are taken by a few Bolters, we can PUBLISH with complete accuracy EXACTLY where those aftermarket running board mounting brackets are placed for a successful install.
The way it works is, people go out and measure where each bolt is (both forward and outward holes) for all three positions. We then argue the little dimensional differences, then we conclude with absolute accuracy where they should be placed and KNOW that if you place them there and they do not fit, there is something ELSE wrong.
I hope I get it figured out too! But we could sure use a couple volunteers with tape measures!
