Changed the backrest out on my drivers seat today.
As usual not as quick as I thought I'd be.:)
The seat cushion adjustment knob is held on by a circlip which icould just get with my finger tips and promptly lost.
You need to take off all the plastic covers on the seat. The one by the seat belt buckle has a screw securing it.
It took me several tries to get the seat back on and the recline to work.
The alignment of the bar through the seatback to the spigot and slots in the rail iso bviously critical. I don't think I got things fully home the first time and the back jammed.
Sweaty work today but worth it in the end.
You are not the first to experience that.
Well documented in here by those that have done it.
HERE (https://www.spyderchat.com/threads/installing-celica-seats.160634/) is a link to a how-to for installing Celica seats, but the same steps would apply if replacing with other MR2 seats.
The shop manual suggests removing the drivers side knob before unbolting the seat cushion, but access to the clip that holds the knob is very difficult. It is easier to remove the knob after the bottom bolts are removed and the cushion can be moved around.