Timing can be tricky. What you want to do well before you pull the distributor is to mark the housing and the flange of the distributor so you index it's position.
If you fail this, get an old distributor cap. Remove your good one. Crash out the #1 post with a punch, and then drill out the hole so it is a BIG hole. Install it onto your distributor. Now you can make sure your rotor is pointing to the #1 post when you install it
Now, get in the car. The distributor's out so it won't start. While you 'bump' the starter (move it ever so slightly with the key) a friend has his finger in the #1 spark plug hole. No I'm not kidding. This will allow you to judge when the compression is 'lost'.
You'll either be timed or damn close to it, or 180* off. If that happens, bump her around the crank again and you've got it
Bear in mid that the cam gear is cut on an angle, and the rotor will rotate slightly as you install it. This is where a lot of mistakes happen- you line up your index marks, but the engine runs like crap...well, the rotor was off a little bit, and you can't advance or retard the spark enough by just turning the distributor to make up the difference. So timing can be tricky, and it's why I always recommend the old distributor cap trick