I clamp a piece of plywood to the underside of the frame then set the seat down on that with a weight in it. If it’s a flat bottom seat the gives you the proper angle and you can easily manupilate it to get the position you want. Generaly as close to the engine as possible then 7 1/4″ from the front of the axle to an area alongide the rear spline of the seat move the ruler up and down 7 1/4″ should be the shortest measurement. Then mearure front the front ear of the seat to the kingpins. the left should be a 1/4″ to 1/2″ shorter than the right. I would put both stays in place you can always loosen one if you need to.