Tj,
The easier check for timing on the exhaust camshaft is to attach a timing light and check timing while cranking the engine. If the distributor is close to the center and the light illuminates the timing marks on the pulley, you know the exhaust valves, at least, are timed correctly.
To check the rest of the valve timing, remove the splash guards under the engine and in the passenger wheel well. Then turn the main crank pulley, the only pulley with two belts attached to it, using a 1 1/4" socket and wrench until the marks cut into the edge of the pulley match up with the marks cast into the lower timing cover when viewed from the top of the engine. Then take off the distributor cap and makesure the rotor is pointing to the contact for Spark plug #1 instead of #3. If it points to #3, turn the engine another 360 degrees. Then remove the valve cover at the top of the engine and look at the camshafts. There are good videos showing how to time pre 1998 KA24DE engines on youtube and you should easily see if something is wrong.
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https://www.youtube.com/watch?v=ofV4eghOP_w]
I spent 15 Saturdays replaced the timing chain and tensioners in my '98 Altima with the engine in the car. It is a lot of work, requiring replacement of the head gasket and removal of 3 of the 4 engne mounts as well as the front to back crossmember that holds up the engine. This is because the lower timing cover cannot be removed without taking both the aluminum and steel oil pans off.
Still if that is your only problem, you can fix it yourself for around $1000 instead of paying a shop double that amount.