The Serial umber is likely to be found on the front face of the bed, below the Headstock.
The Mandrel thread, assuming that it has not been changed, will give an approximate guide to the year of manufacture.
To be more specific, you need to look at Lathes UK, and search for other threads on here about the ML1 – 4 lathes.
All threads will be either BSW or BSF. The Gib adjusters may be BA.
The Headstock is secured to the bed by four 1/4 BSF studs and nuts.
The Tailstock alignment, not the best feature, is by 1/4 BSW. stud and nut.
The Tailstock Barrel is located by a 1/4 BSF grubscrew with the end machined or filed into a key, so some experimentation may be required to get the preferred fit..
The Driving Collars for the Changewheels are secured by 1/4 BSF grubscrews
The Changewheels are locked to the Driving Collars, or to each other (For Compounding ) by 3/32" pins, in blind drillings.
You may well find that the main Leadscrew is Right Hand thread,meaning that two Idlers or Compound gears are required to move the Saddle towards the Headstock.
It may be worth acquiring extra 20T changewheels, and another 60T.
Changewheels from 7 Series can be used, differing only in that the 7 Series used a key, rather than a pin, so that a 3/32" hole will need to be drilled to accept the drive pin.
A 20:60/20:65/20:60 set up (If you can obtain the extra 20T and 60T wheels ) will provide a fine feed of 0.0043"/per rev. This may require some fettling of the Mandrel end of the slot in the banjo to allow the studs to fit to give a suitable backlash for each mesh.
My preference is always to start setting the mesh from the Leadscrew, working back towards the Mandrel; where the Banjo is swung to set the backlash. The studs are adjusted along the Banjo, before it is finally swung up towards the mandrel. Two thicknesses of paper usually suffice to set this.
The Leadscrews on the Cross and Top Slides are 12 tpi, and the dials have 80 graduations, so that each graduation is not exactly 0.001" (0.001041" )
HTH
Howard