a pic of the casting would be helpful.
on the layout table, doing castings approx in the range of 3' x 3' x 3', with cast bosses and bores, it worked like this at least in the 80's
put cstg on table with blocks and 1 jack or more to allow leveling.
put wood scrap targets in the bores. put blue dykem on, let dry, cover with yellow chalk.
use a toe in caliper or scriber to mark the center of the cast bore, but center from the outside of that cast boss, goal is equal wall thickness of the boss when bored, not equal stk removal boring the part necessarily.
level with the jack(s). I was fortunate enough to be using a pdq machine, or portage machine. like a big (6') 3 axis surf gage that had visual scales on all 3 axis, and some rotational capabilities and scales to match too. it followed machined tracks in the table which were a foot apart if I remember, the table was covered in tracks, and you could pull up the roller guides, and re insert them in any track needed, thus maintaining squareness when moving the whole arm setup to extend range if needed.
the casting sat on a big hand rotary table with scale, so it could be spun as you wished.
after leveling the rotary was used to check relationships plane to plane to the center marks you made on the wood. you bumped the casting itself around gently with a soft hammer to establish the best balance between the center marks.
I should have mentioned, before even putting in the wood targets, the general areas of important machined surfaces were painted with a whitewash made of chalk powder and water.
the leveled and balanced casting now could have lines put on the whitewash, to indicate there was stock to mill and bore all around. if not, some retapping, adjusting, and remarking was done to insure 100% stk to finish everywhere.
once good, sent to machining which in those days was manual vtls, hor bore mills, and the casting was set up to your marks and machined. some good drawings would indicate an x, y and z centerline all around the casting, if available, those were put on too.
was a good job, if you failed, you could just repaint and restart.