But first, I replaced the over-long bolts holding the "blocking" to the crossmember in the center bay. I have no idea why such a long bolt (with nut and lock washer against a wood surface) would be used in this application. And -- there was a trim washer on the head end of the bolt. Strange.

After replacing the two long bolts with four #8 x 1-1/2" wood screws, I used the same size screws to be sure the back bottom strip was secure, then marked a cutting line and used a hand saw to cut, and separate, the "back" portion from the "seat" portion.

This is how it looked just prior to making the final saw cut.

Another strange detail is the way the seat back was fastened with over-long bolts to the interior upholstered rails in the boat. The seat back is 64-1/2" wide where its bolt holes are located. This is 2" less than the space between the backing boards of the upholstered side rails. So, if those bolts were tightened, they would pull the seat back frame apart. See a later photo.

Here is the now separated "seat" portion of the front seat frame mounted in the boat. (That's the old and new fuel pump in boxes on the floor, beneath the wheel.)

In the photo below, notice the two long bolts on the floor, and the distance between the holes in the "backing boards" of the upholstered side rails. 2" of spacer material betweem seat back and side rails will be provided so these bolts, when tightened, do not pull the seat back structure apart.

Keep in mind the ski tow ring (when one is found) will be supported by the seat back. This makes me think it would be best to build up the center blocking (in top photo) so the seat back is also supported by the engines (cooling) water distribution (thermostat) housing. Another 1/4" of blocking should do it.

Frank Miklos said on Facebook: That is a BEA air stapler... I use 3/8" and 1/4" staples 7601-20M Stainless steel is available for it ... On these cowls you have to be very careful along the front edge. You have to put the staples on an angle due to the very thin 1/8" plywood..