If you are good at fabing work then almost any tiller can be made to work.
That said the two official tillers for the 318 is the 30 inch hydro tiller. Options are a 12 inch extension and choice of belly drive from the mule drive or rear drive from a dual belt PTO. You can also buy Jim Briney's 3 point mount for the JD 30 hydro tiller if you only want to use the 3 point parts on the tractor-otherwise you need to also use the mounts for the tiller on the tractor as well.
The other tiller is the JD 48 tiller which is mechanical driven and needs the 2000 RPM rear PTO and it has no option but to use the rear 3 point to mount.
Another plus of the 30 hydro tiller is you can turn the tiller around and tine rotation can be flipped depending on soil types. In hard or virgin soil reverse till is what the manual says (in a nut shell anyways). I think the reason is and Hammer down will confirm-hit something hard and it has the power to propell the tractor forward so reversed the tractor is dragging the tiller vs. being pushed by it.
The other option is you get a cheaper deticated rig with tiller on it as you can buy an older tiller/tractor combo for what a 48 and/or 30 hydro sometimes sells for. But you really can't beat the soil prep that at least the 30 hydro does (haven't seen a 48 tiller work yet).
Hello Lukethe hydro is the way to go. a lot easier on the tractor.