Looks like a knurl...
I get that it can make things easier. And, if I owned one, I would likely get plenty of use out of it eventually. But again, the question in point is "Is it necessary?"
I ordered a new dial indicator today. When I get it, I will measure runout and other such things on the DP as well as the x-y table and so on. Once I get these vices tuned up and perhaps level, I will look into proper hardware to connect them to my table. From what my eye tells me I assume the pivot bushing is a 3/32 hole inside a 3/16 rod. That would leave a 3/64" wall. 0.0469 I think I can manage that. I don't have anything 3/16 to try on, but I think I have some 1/4 that I can try on, and possibly turn it down as well.
The other task is the liner relief. Which as far as I can tell is a 0.005 deep race offset around a center point. I assume, that an end mill, will cut on downward contact, like drilling a 0.005 deep hole. If I can control the depth with my stop, or simply the distance from the piece to the end of the end mill, I can certainly mount it to a pin, and offset that pin from center, then just do vertical cuts, and move the piece around the center point a small amount at a time, so that I get overlapping impressions the size of the endmill. If I want critical depth, I can bottom out the cutter on the piece for a zero cut. Then use some 0.005 shim stock to elevate the piece exactly that distance. As I understand it, this distance isn't exactly critical so long as it is greater than 0 and less that something that would be visibly offensive to the eye.
I think, for the moment at least, that I have talked myself out of the necessity of a mill, at least for the time being. I do recognize that dealing with any precision z-axis cutting, I will have to be creative.
I will see if I can reproduce Tony Bose's pivot bushings. Then i will see if i can make proper threaded standoffs for Corby's, and Loveless.
The other task, I am not quite comfortable with would be turning down something from one size to another. e.g. 1/4 - 3/16. But what I think I can do is rig up a live or even dead 60° center that I can mount on the table. I have done something similar before and having the counter pressure seemed to keep it from puking out the MT. Much in the same way that my lathe doesn't puke out the spur drive when I turn between centers. Pretty sure all that will take is something to use as a center that can fit in a bearing, and mount a bearing into a piece of something that can be fixed to the table. One of the guys on one of the machinist groups simply drilled/reamed a MT0 into his DP table, and it can hold s 0 live center. So there's that. None of these ideas are even coming close to $3k so for now these are the kind of things I am considering instead of throwing money at these tasks/problems. The main problems I see with a DP over a Milling machine seem to involve "chuck work" and lateral motion. If I can solve those problems "between centers" then I expand my usage of an existing tool. Money in my pocket! Or at least 3 grand worth of knives I don't have to sell.