Threaded sleeves will reduce the strength somewhat. If you have a mill and rotary table, it would be safer to drill and tap another set of holes for the pins. Another option would be to get M10 x 1 helicoils and a tap and convert the existing holes without loosing any strength.
Threaded sleeves in the chuck body would be satisfactory.
To check how good the chuck is, clamp the jaws tight onto a bar of soft aluminium which has been turned and the witness marks made by the jaws will tell tales.
Edited By old mart on 05/10/2020 15:52:24
Edited By old mart on 05/10/2020 15:57:21