Mark the backbone wires on the burlap/frame where the listing wires will attach (this will tell you exactly where they are when looking down through the slot). Make sure these run approximately with step #3 below, the listing wire sleeve measurements.
Insert listing wires into seat cover sleeves and measure the length of the wires (this is the length of your foam cut).
Measure separation of listing wire sleeves at top and bottom of cover
Transfer top and bottom separation/distance measurements to the foam (Center the separation measurements between guidelines if needed) and make dots.