Our 36" seat came from a new Ford Transit. These are made available by individuals who buy them in bulk from conversion companies as they are not used in the conversions.
The seats came with the mounting tracks however we needed to make some modifications for them to fit the PM. Since one of the tracks was going to be in the "valley" of the floor, a 1/4" steel bar was welded to the bottom to ensure both plate were level and flush with one another. Steel fastener plates were fabricated to be mounted to the bottom of the chassis cross beams. New holes were added to the tracks to accommodate for the spacing of the cross beams. Everything was repainted.
The muffler and heat shield were temporarily removed to make room for us to install the plates. All fixtures were mounted with grade 8 bolts via hols drilled into the floor.