In classic fashion, I think that after literally weeks to months of reading these threads and related searches, I have found a reasonable solution immediately after asking for help on this forum with regards to the "caterpillar" weatherstripping.
Amazon product ASIN B00D0RITMG
The correct term for this type of weatherstrip is called "Pile Weatherstrip". I found what appears to be very close to the correct size at the link I've posted above. I'll update this post when it arrives this week. Who knows what the original pile height was, but I'm measuring mine at about 4mm on the 40 year old weatherstrip, and the old backing appears to be just shy of 7mm. 6.8mm backing and 5.1mm pile height should be close enough.