Everyone is correct, except Boss, well kind of. The same seat was used on the 1x4/1x5 Cub Cadet tractors and the very early 154 lo boy tractors, in 1968 and 1969 only, when that same series Cub Cadet tractors were built. This is also when the 154 lo boy tractors just had the blue stripes on the hood. All of them, cadets and lo boys, the seat could be lifted manually in the back to access the tool box underneath, but there was no specail lever or bracket. The seat mounts just hinged on the front of the tool box, with a steel bar running through them from side to side.
Here is a pic of one on my 124:
And one on a 1969 154 Lo Boy:
In 1970 when they went to the next model 1x6/1x7 Cub Cadets, the 154 got a black striped decal on the hood and all tractors went to a black, high back cushon seat.
That is a really nice find. Even if the fiberglass is cracked, it is easy to repair. DO NOT THROW AWAY THE BLUE BINDING!!!!! That is NLA, and you can scrub it with Simple Green and re-use it. I have a local shop here in Niagara Falls that has recovered several of those seats for me, but you need that blue binding.