I've been to this rodeo several times. #1. Each state/county is different as to what years they smog test, so know the rules of the game before you play. #2 Some states require that all factory emission equipment is in place and functioning (Missouri does this). #3 If you do have to get a smog test, you only have to pass the emission requirements of 1972, not 2016, so you're allowed quite a bit of "smog" in a '72 car. #4 Find out what type of smog test they do in your area. You don't have a computer, so it's not a MIL connector test. Is it just visual? Do they actually put a "sniffer" up the tailpipe? Is the test at idle or on a dyno-type treadmill?
If worse comes to worse & they do use a sniffer, all of your emission stuff is hooked up & working & you fail the smog test then look at the failure test slip & see exactly WHICH part of the test you fail (e.g. hydrocarbons, NOx, CO2, etc.)
Hydrocarbons = fuel, so run the car as lean as you can get it to start. You can also spike your fuel with a lot of alcohol which burns cleaner.
NOx = oxides of nitrogen. These go up as exhaust temperature (& engine temperature) go up, so I'd try to pull out the thermostat & let the engine cool off completely a couple blocks away from the test site, then only run it enough to get it into the test bay (cold engine).
CO2 = I'd have to think about....maybe timing? If you could check your fuel mixture (sniffer or install an O2 sensor), you might be able to tune the engine to minimize CO2.
And as a side note.... in some states you cannot add fuel injection (legally) if the car didn't come with it, add true dual exhaust to a car that only was available with single exhaust, or add an engine that was not available in that car/that year. This means you can't legally put a 440 into a Cordoba that came with a lean-burn 400 (with no 440 option that year).
I played this game many years ago with a 403-Olds Trans Am. I found that if you leave all the stock valve covers & emission stuff in place, block off any unused hoses with pieces of metal rod spliced into the middle of emission hoses to block them off, etc. then you can put a Olds 455 with big-valve Toronado heads in any nobody will be the wiser since as long as you pass the sniffer test ;) in some states requiring visual inspections.
Oh yeah, and with collector insurance you're not limited (in many cases) to any mileage maximum... it's the way you plate the vehicle that matters. In Illinois anyway, you can have collector insurance & normal plates without any mileage limitation. Again, check the rules of the game in Phoenix.