I read somewhere online about this, can’t remember where though.
They said, with secondary removed, to mark a spot inside the OTA, exactly where a laser collimator
should hit when placed in the focuser by measuring down from the front edge of the tube and around the inside of tube. Then put a laser in and see if it hits that spot. If not use shims as Ken suggested to adjust.
Never tried it when I had my Newt but it sounded plausible.
