This is mine, with the vice centred on the available cross slide travel – you can see that it's a fair way from the centre of the tool post (the hole between the two allen screws):

It's fixed using the compound slide mountings on one side, and a couple of tapped holes on the other. The mounting holes are arranged so that the plate can be removed without disturbing the slide. I added a dowel to the back side which, in conjunction with the spigot on the compound mount, ensures that the plate goes back in the same place each time without needing to be trammed in.

I'm sure a proper mill would be better if you have the money/space for one, but this has its uses. 
Edited By Andy_G on 04/02/2021 23:29:07
Edited By Andy_G on 04/02/2021 23:32:02