The Utility Buckets are wider than the sport buckets and the backs do not taper. They have metal backs. If you have the Utility type buckets, there is no one that I am aware of who makes covers. Here is a utility bucket:
There is a member vendor "Truckseats" on the forum that might be able to help you out. There are rear seat covers available from many vendors. The back of the back seat originally had a black vinyl with stripes molded into it. I haven't seen that in a reproduction, but the fronts of the rear seat are close to original.