There were three original types of seats used for the MGA, as shown in the illustration below. The standard Roadster seat is by far the most common and most widely available as used parts. The Coupe and Competition seats are more rare, but these frames can be made by modifying other more common parts.

The picture on the right shows a Roadster seat back frame, driver seat for LHD car or passenger seat for RHD car. Notice the small kick low on the outboard side (near the chassis frame rail), and the larger kick on the inboard side (near the tunnel). This allows it to fit between the chassis side frame and tunnel while being wider across the shoulders. Also notice that the top corner is higher on the inboard side so the curved top of the frame nearly follows the contour of the steel body tonneau behind the seats.

The Coupe seat back frame is not higher on the inboard side, being equal height at the shoulders. This part can be fabricated from the Roadster frame by cutting the inboard tube at the widest part of the frame, and also the two vertical tubes (an inch or two from the top works well). Remove a short section from each of the three tubes, just enough to push the inboard shoulder down to be equal height with the outboard shoulder, and to have the two vertical tubes the same length. Then weld the tubes back together, and you have a Coupe seat back frame.

Once you have the appropriate back frame for each seat type, the Roadster and Coupe seats can use the same bottom frame, bottom board structure, and molded foam cushion. They can also use the same backboard and horsehair inner pads with appropriate trimming to fit the frame shape. The leather covers will have a different pleating pattern as shown above, but otherwise the Coupe seats assemble in the same manner as the Roadster seats.

The Competition Deluxe seat frame is considerably different, squared off across the top, and having a totally different base frame. This one is easier to fabricate by modifying the frame from an early MGB seat. Starting with the MGB seat frame, cut one inch out of all the cross tubes, back and bottom, to make the frame one inch narrower. Weld that back together and you have a nice frame for the MGA Competition type seat. Beware this may require relocating the slide rails on the floor, but I haven't verified that yet.

The Competition seats assemble more like the MGB seats. These do not have the wood baseboard structure, but use webbing stretched across the base frame with the foam cushion resting on the webbing. The foam seat cushion is different, as well as the backrest padding. See several pages to follow.