Rugo, I don't have a clue what parts you are talking about but everybody keep in mind. Most parts have been tweaked early on by the manufacturer as to actual physical fit to our trucks. Mistakes found and corrected.
Our Trucks, when new, were built with parts that had huge 40's and 50's manufacturing tolerances and the assembly of the truck (gaps and other dimensions) have large tolerances.(FAM) If you have plus or minus 1/8 you have trucks that can be 1/4 off from one to the other. From one side to the other! Our trucks wear, sag, get in accidents, get bent (overloaded), twisted (dog track), repaired, rebuilt, lifted, bagged, lowered, clipped... the glass thickness has changed. The manufacturers of our parts have built parts to a nominal dimension and we try to install on a plus or minus, rearranged, deranged truck. You gotta make do with what you got when you get what you buy when you keep doing what you are building to get where you want.
Whip it, whip it good, bend it, tweak it, make it fit...Whip it. Straighten it up, weld it up, move forward, build it. Whip it into shape...
The actual material/compounds, that some of our parts are made from, is a different story than fit. TWO separate issues. Carl didn't say his gaskets didn't fit.