Inside cab weather strip

My '54 R has a c-channel all the way around the doors on the INSIDE of the cab. The original stuff was basically gone due to rot and wear. I bought the $700 complete weather strip kit and I am very happy whit it BUT it did not have this seal. My '51 L series doesn’t even have the channel in it at all so I'm wondering if it's something introduced later or in a more fancy package or something? The weather strip has a "T" shape on the back/inside to fit in the c-channel and I'm GUESSING an oversized probably "D" shape on the other side to help seal around the door? Does anyone know what this stuff is called or even better where I might be able to find some? The entire cab is painted and completely reassembled now so it's too late to just cut this channel out of the truck and I'd rather do it the right way anyways. Any help, advice, or maybe a link would be appreciated! Thanks again!

Your post is not clear about what you are looking for. I am adding a picture from an IH parts catalogue. Maybe you could note one of the part numbers to make this more clear.

This what is in my S series trucks.

The pic of the S series looks like it would be the one. I was guessing at the shape but that looks like it would fit in the channel and then extend out to the inside of the door frame. Where did you find that??

I think you're looking for Clester's Auto Rubber Seal #8305-3114.

I just did these in my truck, it is a L with a S cab, like noted earlier cab didn't have it.

according to shop manual you start at top split in channel toward front of cab, you feed down to back first and then down to front, then shove last little bit in at split channel,

total pain to install, need LOTS of soapy water or equivalent type lube, extremely hard to do, I finally clamped end of it with vice grips to get a better pull,
have to feed it in at channel split while pulling down the track making sure it doesn't come out,

once in place need to make sure it is relaxed and not stretched anywhere, vice grips damaged the end, but it comes slightly long and you have to trim some off anyway,

I strongly recommend rubber lube for that kind of thing. See if your local tire shop will give you a "dixie cup" of the stuff. There are work arounds, but none work as good as rubber lube. Dish or laundry detergent works for a while but gets sticky. Rubber lube stays soft and slippery pretty much indefinitely, it is great for tires, O rings and rubber seals. Looks like a soft "grease" but has the constancy of Go-jo.

THANKS AGAIN!!! Especially to 56-S-Fan and PaulH. Exactly what I was looking for! ordered and expected Thursday. Now the wait and joy to try and install it. I really appreciate the install tips as well!