Hi Graz,
I have put a post on the Drummond Forum but in case you can't find it...
On the back end of the mandrel are 2 plain collars. The outer has a pin that locates with the change wheel. The inner is threaded with a grub screw in the side. This is for adjusting the end float.

Undo the grub screw and loosen the collar.
On the outside ends of the headstock are screwheads.

These will pull against rings on the inside which pull the conical bearings into the tapers of the headstock casting.

To tighten the bearings, adjust the screws by screwing them in. Be careful!
Make sure that you keep both sides equal!!!! Watch that the rings remain square to the casting!
When you are satisfied with the adjustment, tighten the back end collar to set endfloat and do up the grubscrew.
It is worth placing a small brass or copper end cap to the grubscrew so that it does not damage the thread when you do it up.
I'm afraid that, with a 100 year old lathe, it is a matter of trial and error to find what suits your machine best.
At least, I have not heard of hard and fast settings.
One thing to watch for is heating of the bearings, easily checked by putting your hand to the headstock casting.
My longbed B (the scruffy one in the photos) is a bit temperamental on the left bearing, so needs a bit more slack than the right.
I use cheap new (!!!) multigrade petrol engine oil to lubricate....and for goodness sake, don't forget to lubricate the backgear shaft!!!! You can see the oil holes easily.
Others may criticise the choice of oil but it is cheap and maintains viscosity through winter and summer. (Do not use diesel engine oil as it contains detergent!) My workshop is not heated...and it does not suffer with condensation with plenty of ventilation! Just run the lathe for a few minutes before working in the winter cold to warm the bearings if you are in the same position.
Hope this helps
Andy
PS just seen the photos (thanks guys for showing me how to do this) and I am sorry for the crap quality.

That is camera phone too close

If you can't see what I am trying to show you, please let me know and I will PM the pictures to you.