How was the rear mounting plate (by pulleys) attached to the rear of the tractor? There has to be something to give support and for tension on the pulleys. I believe that is where your issue lies.
I found this which shows pulleys/mounting bracket, which has to bolt to the rear axle of the 316, just like the gearbox of the 2000 RPM PTO.
Clutch:
More investigation, downloaded all the Owners Manuals for the 30 Hydro Tiller, to find that yours was originally for the 420/430 with rear PTO option, I have attached the pdf
I found this which shows pulleys/mounting bracket, which has to bolt to the rear axle of the 316, just like the gearbox of the 2000 RPM PTO.
Clutch:
More investigation, downloaded all the Owners Manuals for the 30 Hydro Tiller, to find that yours was originally for the 420/430 with rear PTO option, I have attached the pdf