I am not certain if the 34 ferules are the same as those used on 41 trucks...if not disregard the following.
I recently bought some from one of the vendors (classic Chevy I think). These were not exactly like the originals in that they had a rubber grommet that fit over the metal. This rubber enabled the ferule to fit over the door without scratching paint. I think they worked very well (how often do we say that about reproduction parts?!). I borrowed one of the "much maligned" ferule tools from a friend and had much trepidation in using it as I had never heard much good about the tool. I found that crimping just a little at a time and rotating the ferule tool around 3-4 times making slightly tighter crimps that ultimately snugged the ferule to the door quite well. I suppose the ferule could be installed without removing the door panel, but I don't see how the old one could be removed. With the door panel installed, it would be difficult to observe the amount the ferule is being pinched as one progressively rotates around.
