Fuel filter is by the driver side fender - just forward of the master brake cylinder. One of those inline canister types - might need to soak it first with some pentrating lube, like PB Blaster, as those fittings are usually quite corroded.
But since you got a pop or backfire after you cranked it for a while, sounds like more like a timing or ignition issue. Might help to pull the plugs after you cranked it for a while to see if the plugs are gas/oil fouled or completely dry. That will indicate if you got fuel. Now to check on fire (ignition) - might be helpful to crank the engine over with the hood up in complete darkness to observe any arcing that can occur with bad plug wires or faulty ignition systems. MIght have to pop off the distributor cap and check cap and rotor for significant carbon deposits, arcing, burned contacts, etc.
Any restrictions in the induction system (intake manifold, air filter, etc.) can also give you a hard starting condition. Make sure the filter is clean and nothing seems to be amiss with that system.
Timing is the last thing to check - but I would check the easy \"free\" stuff first.