From
https://www.model-engineer.co.uk/forums/postings.asp?th=171047Myford used three different spindle nose threads for the ML4, all Whitworth profile:
Earlier ones were 7/8" x 9tpi or 7/8" x 12 tpi.
Later ones were 1 1/8" x 12 tpi, the same as the ML7 but with a smaller register diameter ( 1 1/8" instead of 1 1/4" ).This might help on thread on ML4 headstocks GB - but doesn't look as straightforward as we'd have hoped! This will affect availability of faceplates as well as chuck - fingers crossed you have the ML7 version even if there's a small register issue to deal with.
Richard L's knurler is similar in principle to the one I use - a bought one that wasn't too silly a price, but can't remember who from. A clampy one is, I think, a whole lot easier to use than a wheel or wheels shoved in by the topslide, which will necessitate the use of a fixed or travelling steady to maintain pressure on anything that isn't chunky.
A running centre shouldn't set you back that much, for a reasonable quality one. Lots to choose from, at least. And better than using a fixed 'half-centre' and loads of lube, certainly.
The topslide does seem close to centre height on them, as chaterlea remarked. Which poses a problem for a non-Myford toolpost perhaps. Nonetheless, it would probably be possible to make a four-way one to take certain sized tooling. For my 7 I used a cube of mild steel to make a 4-way (no register underneath on the slide, so it sits anywhere you want) and a different much chunkier single tool holder - but it does need a miller or access to one to do a half-decent job.
