1996 Subaru Outback Hex Key Size

Don't mess with those, the block drain is a draincock at the back of the engine as shown here:

DRAINING & REFILLING COOLING SYSTEM 1. Lift vehicle. 2. Fit vinyl tube to drain pipe. See Fig. 12 . Fig. 12: Draining Engine Coolant Courtesy of SUBARU OF AMERICA, INC. 3. Remove radiator cap to drain engine coolant faster. Loosen drain cock to drain engine coolant into a container. 4. Remove air vent plug from radiator. See Fig. 13 . Fig. 13: Filling Engine Coolant Courtesy of SUBARU OF AMERICA, INC. 5. Fill engine coolant up to filler neck position of radiator. 6. Fill engine coolant to upper level (full line) of reservoir tank. 7. Close both the radiator cap and the reservoir tank cap properly. 8. Reinstall air vent plug. 9. Run engine for more than five minutes at 2000 to 3000 RPM, until engine is completely warm. 10. Stop engine. Before inspecting fluids, allow temperature to drop to a safe level and perform the following procedure: Ã Â Â Add engine coolant to filler neck position if levels have dropped in the radiator. Ã Â Â Add engine coolant to upper level (full line) if levels have dropped in the reservoir tank. Ã Â Â Close both the radiator cap and the reservoir tank cap properly.
as far as the EGR torque, no more than 44 inch lbs, but just snug it evenly, people break em when they tighten one side then the other, finger tighten both then just snug each one a bit more with the wrench EVENLY!

44 inch lbs is the max torque for any part bolted to the aluminum manifold. All you need to do is snug it until no vacuum leaks out. I will investigate the hex caps further, get right back.

Here's what Mitchell shows for the job:
INTAKE MANIFOLD Removal 1. Release fuel pressure. See FUEL PRESSURE RELEASE. Disconnect battery negative cable. Drain engine coolant. Remove air intake/upper air cleaner cover assembly. Disconnect accelerator cable. Disconnect cruise control cable (if equipped). 2. Remove accessory drive belt cover and belts. Remove power steering pump with hoses attached and set aside. Remove generator and bracket. Disconnect PCV, EVAP and brake booster hoses. Disconnect spark plug wires. Disconnect coolant hoses from throttle body and idle air control valve. 3. Remove EGR pipe. Remove engine wire harness connectors and bracket. Disconnect electrical connectors from coolant temperature sensor, knock sensor, camshaft/crankshaft position sensors and oil pressure switch. Disconnect fuel hoses from pipes. Remove intake manifold. Installation To install, reverse removal procedure. Use NEW gaskets. Tighten all bolts/nuts to specification. See TORQUE SPECIFICATIONS.

After a quick call to Sub service the size wrench is 14 mm hex.

If you need any thing just call! Good luck and hone those skills!