1970 Front bucket seatbelts

That makes sense, the longer sleeve helps get the belt in between the bottom and top of the rear seat. And the short plastic sleeve helps keep the belt tight to the side of the bucket. Not sure where your going with this? Is there a difference in belt size or length if the car was originally a bucket seat car or bench?
Bucket seats don't get retractors on my 71. The bench seat did. The bucket seat cars just get a belt with a plastic cover. The belts that were on my factory 71 demon for buckets was about the same length as the center rear back seat belt. I slipped a plastic cover on it from the outer rear seat belt after cutting the cover to the same length as the bucket seat belts I have for the Demon. You can't tell the difference. I looked for seat belt sets for sale on the web . None listed that I saw were correct for the front buckets. You would have to buy three sets to make the two belts you need for the front. You only get one center rear belt per set.