I don't think so. I have both blades and have a 316 and 425 now. I bought the blade for the 425 then got a Kubota so haven't ever put it on. The frame on the 425 I believe is wider. The 318 blade is a one piece with its own hydraulic cylinders. The blade for the 425 uses a separate mount between tractor and blade that has the hydraulic cylinders on it. This was an improvement so you could have a broom or snowblower and each attachment wouldn't have to have hydraulic cylinders. The hoses also need to be longer for the 425 to the connections.
Would be simple enough to make either one work on the other tractor but not to remove from one to connect to the other.
So in answer to your question I don't think they are interchangeable the way I think your asking. I can't measure them as they are at different location.
Anybody interested I would sell either. In Eastern Iowa.
Like Capt Dan said not without modifying the mounting brackets. My son did this conversion and while it wasn't difficult it did move the blade farther forward which takes even more weight off the rear wheels and tends to push the front even more when angled.
It might possibly, if you do it qwik-tatch method for both tractors. But the qwik-tatch, would be custom made for the front of each tractor, especially the 318. Then other items could be added besides blade.