Probably too late for this poster but maybe it will help somebody else. For one thing, the most likely reason this didn't get a reply is that such questions are usually posted and fielded on the firearms forum relating to the accessories.
The Yugoslav M48's sling was modeled on the German K98rifle's sling. The stock buckle was the same but, the strap was plain and only secured at the opposite end with a brass button. The strap of the sling was about 1/8" thick- what we now call 7-8oz, oil tanned leather 1" wide by 47" long.
Here's one on my M48B.
Attachment 92952