OK I'll try to give you a step by step here:
1. Remove the old distributor cap and spark plug wires making note of where the cylinder number 1 wire is located on the cap AND where the body of the distributor is pointing.
2. Disconnect the wires from the coil and tape them out of the way (they will not be used with eth HEI). Separate your tach wire for reuse.
3. Remove the coil and bracket from the engine.
4. Remove the vacuum advance hose from the distributor and plug it with a screw.
5. Remove the distributor hold-down clamp.
6. Note the direction the rotor is pointing, then lift the old distributor straight out.
7. Route a new power wire from the fuse box "IGN" terminal, through the firewall to where the distributor will go. It should be a medium to heavy gauge wire. NOTE: the IGN terminal is a spare male spade connector in the bottom center of the fuse box.
8. With the distributor cap removed, lower the new distributor into the engine (make sure you have a new gasket on the distrubutor). Keep in mind that you want the rotor to point the same direction as the old rotor. Also be aware that the rotor will start to turn clockwise when the distributor gear engages the camshaft gear.
NOTE: if the distributor does not sit flush with the intake the most likely cause is the slot on the oil pump drive shaft is not aligned with the drive pin in the bottom of the distributor. You can turn the oil pump drive shaft with a long screwdriver if necessary.
9. Reinstall the distributor hold down clamp. Leave it loose enough so you can turn the distributor housing.
10. Install the cap and wires. Rotate the distributor housing so that the terminial for cylinder number 1 is pointing to the same spot it was with the old distributor. Usually cylinder number one is in the front of the cap on the driver's side (pointing at the drivers head light).
11. Connect the three wire connector from the distributor into the distributor cap and connect the new power wire to the + terminal on the cap. If you have a tachometer reconnect the old tachometer wire to the "-" or "tach" terminal on the cap.
12. Fire the engine and set the timing.
13. Reconnect the vacuum advance hose.
14. Fully tighten the distributor clamp bolt.
Hope this helps.
68 Camaro, 383 small block with TH350 trans. 11.98's at 111mph and never trailered.