I just checked my '74 145 and the seat tracks bolt to a large "U" shaped tubing, and then that, bolts to the floor. My '83 245 seat tracks bolt directly to the floor. The spacing of the tracks, center to center on the 145 is 15".... on the 245, C-to-C, is 14-1/2".

If you have a gas or arc welder, it looks like you could mount 240 series seat tracks onto the top of the original "U" shaped tubing arrangement used in the 140 series. By welding a simple piece of angle iron to the 240 track bottom, you could position it, before welding, to account for the difference in the width. Incidently, the dimension from the bottom of the seat tracks up to the top of the seat cushion, are the same on both cars, at 7-8". Tom