My limited experience:
Bought a field-rescued '28 Special Coupe in 2009: Cosmetically freshened ( new interior, new topping, primed and painted rattle-can black), original running gear made to function. Nothing was "restored" or rebuilt to factory specs; it was still "tired iron".
Odometer was showing 77,000 miles, speedo unit still sealed, date stamp agrees with manufacturing period of engine, gas-tank stamp, etc. - believe this to be authentic mileage.
Engine still un-bored ( original pistons and valves, pistons showing plenty of "Side-slop" at top of bores), would still pull 60-65 psi compression, warm.
I drove this car daily for 1.5 years, 2010 ( through the winter too ) through fall of 2012. At least 50 miles a day. Put about 11,000 miles on it.
Had some teething pains: head gasket blew and got replaced. ( no more trouble ), rotten 1940's aftermarket radiator (Kramer, Trenton, NJ ) caused some overheating issues, replaced with Brassworks HD (problems resolved), then piddling things like replacing worn brake tracks, brake adjustment, carb overhaul, headlight wiring (crappy repro connector plugs), replacing missing cotter pins through-out...
Except for the above-mentioned issues, most of my driving was trouble-free, and the only time I "came home on the hook", was returning to Scranton from Macungie 2011, during an incredible monsoon - car started to misfire after Lehighton exit on the PA Turnpike NE Extension, and I limped along the shoulder until the Service Plaza at White Haven... it seemed that water was flowing down the repro ignition conduit into the distributor, shorting the condensor. It was still monsooning, so I couldn't get the ignition dried out. After an hour of playing with it in the parking lot, I gave-up and made the rest of the trip on a flat-bed.
What finally sidelined the old girl was another trip on the NE Turnpike. At my fuel & oil stop before returning home, I mistakenly put a crumpled paper-towel in the top of the oil fill tube to reduce oil-spray under the hood. It created enough back-pressure for the blow-by to force the engine oil out the rear main. I didn't know what the problem was until rods started pounding about 40 miles from home. (Low oil, rods #1 and #2 starved for oil, burned-out the babbitt. Operator error. ). Babied it the last 40 miles home, praying it wouldn't throw a rod, and parked it. That was fall of 2012. 87,000 miles. It will still start and run.
If I hadn't blocked that breather tube, I might still be driving it.
Now waiting for Schwalm's to finish rebuild on a diamond block replacement engine.
If a Model A Ford had received the best of maintenance and was not abused in service, I don't see why they couldn't run close to 100,000 miles...
If you rebuild one stock, and equip it with a modern air filter, run detergent multi-weight oil, and keep it well lubed, it should easily last 75,000 miles....
Back in the old days, it was common for cars to need a valve-grind every 10-20,000 miles, and a re-ring around 30,000 miles.
In college, I acquired and drove a '48 Chrysler New Yorker. During its resurrection, I had to pull the cylinder head to fix some stuck valves, and was surprised to find that the engine had been bored 0.030", with only 76,000 miles on the odometer.