Go with the manufacturers specs for sure.
The 130 ft-lb head bolts are 9/16" so yours are probably 1/2" but you can torque them to higher than 75%. They chose 75% to be safe based on torque wrench and friction variations.
Turn of the nut method is now preferred and I see even GM specs it that way in the Service Manuals. You can safely go to 85%.
Some fasteners are even torque to yield for one time use but they are made of a special metal.
You could do a simple calculation to determine turn of the nut if you knew the value of the studs yield strength and the number of threads per inch, the rest is engineering physics