Ok,, just for reference for others in the future who find this thead... or do a search ....
The valve adjustment on these old overhead cam diesels is done by adjusting the position of a nut which is threaded on the actual valve.... the valve has a slot in it and a wider nut at the bottom of the adjustment stuff but above the valve seals...has a tang which fits into this slot..... it can rotate with the valve rotators fitted in most of these engines.. but allows a way to ' clamp ' the valve rotation for adjusting purposes...
In the event that the top nut or the next lower nut ( which is used to lock the top nut at the proper height ) are stuck... the wider, slotted nut is used to hold the valve from rotating so the upper two can be set and locked together...
That is why you sometimes see people post saying that they have never had any problems and don't need any way to hold the lowest nut. But , IF just ONE valve adjuster nut is STUCK.. then you need that lower one to get it loose enough to move.
Most people find that the bought lower wrench, due to it haveing a ' stand' which holds it at about the right position.. plus some combination of to bent wrenches ( I got Crasftsman and bent them myself ( being cheap ) are very helpful for doing the valve adjustment.... But I bought the lower one after trying and failing to make it ...
I am sure we will have several posts now saying basically " you wimps" ' I have always used plain wrenches and have never needed to hold the bottom nut'..... LOL