I had a similar problem where I had to adapt the vertical milling slide to clamp to my cross slide. This was time consuming to fit and not a pleasing experience.
I had exactly the same experience when I bought a quite expensive vertical milling slide – I could not find a way of securing it to the cross slide (table) – I solved the problem by making a boring table – simply a flat steel block of approx same surface area ( ~8" x 6"
as the cross slide and 20mm thick. I hold this down on the cross slide with four t-nuts in the cross slide t-slots and 8mm hex headed bolts going down though the boring table. Metal suppliers will pre-cut metal to your requirements. I haven't been at this for long but I believe that most experienced engineers will have one of these in their tool set – whether home made or ready made.
I then bored the required threaded holes (three in this case) in the boring table to hold the vertical milling vice. This makes attachment and detachment much faster and has avoided the temptation to drill holes in the cross slide table.
I have also found the boring table useful for fitting and raising other accessories – including dividing head and slitting saw table. With suitably placed threaded holes it can also be used for raising and holding work pieces during boring operations (and many other operations) – as it's name implies !!!!
I don't have a Myford lathe but I see that ready made boring tables are available to fit Myfords (e.g. eBay). The only difference is likely to be the distance between the t-slots.
The manufacturer of my Lathe recently starting supplying a specific Myford style Milling Slide for my lathe – it comes with a raising plate very similar to the boring table I describe above – it is wonderful – and it also holds a rear tool post – Christmas has come early !!! But my boring table still comes in very useful for other operations.