Old BushHogs

I own 2 old BushHog brand BushHogs. One is 5’ the other 6’. These are old models and very heavy units, no leaks I’ve had a couple welding repairs done as the bracing on these old hogs create some drainage issues. I purchased both these from the original owners in the original condition (no modifications) as purchased from the same local BushHog dealer. My problem or discussion is neither have a driveline clutch or shear bolt on them. I posted in another forum and got nothing positive. I was told someone had modified them, and this was not factory etc. I told them I had spoke with a older BushHog representative at the National Farm Machinery Show in Louisville, Ky. and that BH had indeed offered these units without a driveline clutch or shear pin. I would like to put and inline clutch on these BH’s however I’m having a problem finding the clutch I need. I’m hoping I wouldn’t have to replace the whole driveshaft. $$$$.
The drive shaft has the 6 spline with the detent on the PTO end. At the BH gearbox end it has a 6 spline with just a hold thru bolt. I cannot find a clutch with this combination. Anyone got any thoughts. I run these units with an older 35 HP diesel.

Old BushHogs