Is there a special wrench for tightening the head nuts on a Ferguson 35?
Offset adapters are available from tool suppliers like Snap On, Mac Tools, etc.
One of the adapters I use is Snap On part # SRES 22 6 or 9. I can’t make out the last digit stamped on the tool. This tool is a bar approximately 3 1/2″ long with an 11/16″ box end wrench in one end, and a 1/2″ square cutout at the other end for a 1/2″ drive torque wrench or breaker bar. This same tool should be used to torque all the nuts when installing the cylinder head.
The TEA-20 gas (petrol) Standard Motors engine, the TO-35 diesel Standard Motors engine, and the MF-35 diesel Perkins diesel engine all have 7/16″ head bolts/nuts with 11/16″ AF (Across Flats) heads. Therefore the 11/16″ adapter used on the Continental Z series engines can be used on all these engines. The adapters are available in a range of sizes to fit most all sizes of bolts and nuts used on cylinder heads.
Years ago mechanics sometimes used a 1/2″ drive, 11/16″ crowfoot socket. The problem with this tool is a crowfoot socket is essentially an open end wrench, and the jaws of open end wrenches tend to spread when torque is applied causing the wrench to either slip off, or round off the corners of the nut.
I have also seen home made offset adapters, but the Snap On adapter is probably your best bet.