If you clamp a DTI holder in the chuck you can bring the turret in and sweep round the ID of the drill holder and offset the X to get it centred.
A better approach would be to turn up an accurate bar to fit in the drill holder and sweep the OD of the bar, you can then also run along the length of the bar to check the alignment of the turret. Running along the length would actually be best as the first step as you can adjust the turret if needed then you can sweep the OD of the bar to find X centre. If the height of the drill holder is out there is likely not much you can do about that unless there is some way to adjust the height of the turret, shimming would work but could lead to less rigidity so I would only do that if it is well off.
 Normally if you make up drill holders you would bore and finish them to size fitted to the lathe, first by drilling with a drill in the chuck then either a reamer or a boring head in the chuck to get to final size, that ensures the holder is exactly centre.

I have often thought of making a part catcher for my lathe but as I mostly do one off parts I dont really need it, would just be nice to have one for the occasional longer runs of parts.

Hood

Hood, I aligned the turret when I put the lathe together and I used the method you mentioned....using a ground rod and indicating its length.

As for your thoughts on the holders...now why didn't I think of that   I made holders for the Emco's on my old manual lathe, never thinking of finishing them off on the Emco's, to get them accurate .....   this old age stuff, sometimes the brain needs to be kick started ...  lol

thanks
pete

Depending on whether you are using sleeves or not, it may still be possible to finish off on the lathe. If say your ID of the holders were 25mm Dia and you could take out to 30,  you could just make your reducing sleeves to suit.
You may find however you are fine in height and its just the X axis that needs set correctly thus only your offset needs tweaked in Mach


Hood

Hello Hood, I fixed the problem . Dummy me assumed that when I removed the turret and replaced it with another Emco turret I had, everything would fall back into place perfectly... I was a bit wrong in that assumption....lol. The newer turret needed an additional .018" worth of shim to get things centered. It took a bit, but, now it cuts the way it should, smoothly and on center

I'm telling you this old age stuff is not for the weak...lol

thanks for jarring my brain cells

pete

Good you got it, your drills will last much longer now
Hood