Hello,
unfortunately,there is no easy way to take the drive for the tachometer from a 6cyl pump as they have never been built to do that.
And you don't tell which pump or engine you have.But assuming you are talking of a 590e engine,the Minimec pump camshaft will always have a splined end protruding from the pump to drive the exhauster but with no provision for the cable holder and no square hole to take the cable.If you have an earlier pump (SPE) they will also have a drive for the exhauster (coupling like the front one ,pumps with pneumatic governor) or a mechanical governor (no acces to the camshaft).
The Fordson pump has a special camshaft, a special pump cover plate, and a special support to screw the cable .The tachometer is also special (counterclockwise ) as well as the cable.
Look at the pictures,the square tachometer drive on the camshaft is a real weak point of the pump and can break easily.It is very badly conceived:the end of the camshaft is bored round and turned to a small diameter.Then this little cylinder is pressed to form a square (outside and inside).Unfortunately the resulting square inside is not so square as it should be and the cable will eventually turn loose.Especially after 50 years of use.
Another problem is that there are no true Super Major counterclockwise tachometer remanufactured.All the ones for sale (even those marked as "like original" ) are the Dexta type .The hour counter does not have the same ratio and there is no RPTO (Raised Power Take Off) mark.
You will probably have to take the drive from the engine,but the cable must be longer than the original, and the (new)angle drives available on the market are of appaling quality (at least the one I got)
P.S. It seems that my pictures don't show in full size,don't know why ,while others are much bigger and show well????