A lot of what is explained here may seem incomprehensible until you have taken a seat apart… then it all becomes… a bit clearer.
I was getting nowhere with the cushion so turned my attention to the seat back. My first attempt at inserting the seat covers into the groove in the back of the seat was frustrating as I needed about a half inch more of slack. I regrouped and decided to attach the clips on the bottom that hold the front and back of the cover on each side.
I made up a tool to help pull one clip towards the other than I was able to get them attached using 90 degree needle nose pliers.
Next I set up a small heater to warm up the head rest section, front and back. After leaving the heater do its thing for a half an hour I was able to pull the top part of the back of the cover down and insert it in the grove enough to hold it, then working with a screw driver then my fingers I was able to work it properly in place all the way around. A bit like installing a bicycle tire.
I then installed the heater on the headrest to warm up the interior of the seat.
While test fitting the cover on the bolsters I found that foam moved around so I taped it in place.
I had trouble inserting the tongue into the 2 clips at the top, so I removed clips from the frame and attached them to the seat and then reinstalled them on the frame. Much easier.
Note: the clips were deformed during removal of the old seat cover, so make sure to bend them back together.
For the sides I started by removing the clips to attach them to the cover like at the top… but when I tried to reinstall the clips to the back there was no way I was going to be able to pull enough slack.
Even forcing the black band on what I call the tongue was not going to reach the clip...
So I looked for a way to use zip ties again… their big advantage is that they can be attached with lots of slack then pulled tight and it allows for slight differences in the size of the cover.
This is what I came up with…
... a piece of wire threaded through the channel that the seat back of the cover is pushed into, then zip ties up to the tongues that normally are pushed into the clips. The 2 zips nearest the bottom cushion can be attached to a metal bracket on the frame.
The zip ties can be tightened progressively and then the seat can be assembled. At a later date, when the leather has stretched it can be re-tensioned by just removing the middle insert and tightening up the zips.
I did all this with the cover partially installed… for the passenger seat I will install the wire for the zip ties before inserting the seat back into the groove.