I keep a Taig lathe tool post mounted on the spindle housing (fits in the t slots) and use that to secure a dial test indicator holder (cam lock style with round stock mount not mag base). They are meant to mount in the spindle but the 1/4 inch tool post works well. You want the mini version of the holder though, think I got mine at little machine shop some time ago.
Note: you probably want to use a dial test indicator rather than dial indicator for vise squaring.