There are dots on the front of the timing chain gears . Make sure the dot on the bottom gear is at 12:00 and the cam (top) gear dot is at 6:00 and that they are perfectly alighned . To put the distributor in , put the number one piston at top dead center . This is the cylinder at the front of the car on the passenger side . You said your replacing the cam , so I'm assuming the intake manifold is off the car . after the timing chain is put on correctly turn the crankshaft until the number one piston is all the way up and both valves are closed . you can verify both valves closed by the lifters . if neither lifter is up for the number one cylinder and the piston is all the way up then you have it in place . Now you need to make sure the balancer is at " 0 " on the timing mark . You may need to move the crank just a little to get it there . Then put the intake back on and drop the distributor in and make sure the rotor is pointing to the number one terminal on the cap . leave the hold down bolt loose for the distributor because you will still need to time it with a timing light . But you should be pretty close . If you have any questions , just post up
302 timing chain markings 
