The headers thing is bs. As long as you don't have a leak, you should be fine. I remember 1968 is an important year for smog, I just can't remember if it's when cars started coming with smog equipment from the factory, or if 1968 is the year that cars are subject to the required smog equipment under the hood. 1982 and newer vehicles are subject to an emissions test (if inspection station is equipped), so just keep going to the small gas stations that only do safety inspections. I believe Dallas is using an ASM test (where they put your car on the dyno and use the sniffer), so I'd stay the hell away from there . Other than that, an air cleaner will not fail inspection (from what I remember), but I do remember something about a hot air riser -- I'm just not used to working with them. All I can remember is that it's something that is supposed to route warm air to the carburetor for emissions purposes, I believe.
If I remember correctly, the only thing under the hood you're supposed to have a smog pump, egr valve/tube/etc., good belts, non-leaking master cylinder with proper fluid level, and non-leaking p/s pump with proper fluid level (to hell with the alternator, waterpump, etc.) All I've done in the past was just slip them a few extra $$$ and they wouldn't argue. Sounds like your last gas station will be your best bet.