Hi Mark,
I've been chasing this question for the last couple of days and reviewed a lot of pictures. I agree the Tandam Associates site seems to be misleading. The picture they show that says it is the longer feather appears to be the shorter feather.
From the pictures I've gone over as best as possible. It appears to be that the short feather, on the right side, ends at about the start of the "B" in built. The longer feather seems to end at about the "I" in built.
Of course this is only my observation. There doesn't appear to be a definitive source for this information. I've found the Tandam website to be helpful but not always accurate. I was also looking up 6464-425 NH boxcars. I was going through a collection I recently bought that has 20 6464 series boxcars in it. The 6464-425 is on a Type IIB shell, which Tandam does not identify as a variation. I thought maybe I struck gold but of course, on further research I found that it was produced on the Type IIB shell. Of course, I'm not necessarily picking on the Tandam website as they are extremely useful in research. Even their site mentions to not take them as the be-all, end-all information source.
I hope this helps. BTW, the one I was researching appears to be the long feather version on a Type I shell with the long yellow/orange feather. The Type 1 is somewhat scarce so I guess instead of gold, I may have at least struck bronze.
The rest of the 6464 cars in the collection were mostly C7 to C8 but I already have these in my collection in this condition. I'm just going through to compare what I bought to what I have to see if there is an opportunity to upgrade my collection.
LionelFlyer