You say this motor has never been out of the car. You MUST check if you have the stock single roller aluminum w/ nylon teeth cam gear as it will cause your low vacuum issue as well as cylinder pressure issues due to retarded cam timing. If it's still in there get rid of it. Check this way: pull the distributor cap and watch the rotor as you grab the fan belt on both sides of crank pulley. Pull the belt so's crank spins in reverse direction of normal rotation. If you spin the crank more than 5 degrees without the distributor rotor moving- you've found your problem.