Not clear what u intend to do here?
As the lever does not touch the stop screw when u connected the vac supply direct to the actuator (measured at 28"Hg) and actuator does not hold vacuum, yes you most likely need a new vac actuator.
Need a hand operated vac pump to set actuator rod length (makes is a lot easier). Also can be used to check the diaphragm in the actuator for leaks.
Need to remove you current actuator and check that actuator lever can move freely all the way up to the stop screw. Check for vane operation.