So random people shouting out their fuel mileage is kind of a useless.
There are so many variables as pointed out.
So on my brothers car we know it has a used B cam, a B dist cam, not sure of the pistons but the engine only had 40,000 miles on it. The block was cleared of all crap in the heat jacket, you might be surprised how much can come out of a block. Factory carb, fan, brakes that are well set up- able to take the car from 60 down to 30 on the highway around Chicago when the A hole takes the on ramp, cuts in front and slows down rapidly. They do not drag.
The car had crappy babbitt done by a shop known for failing babbitt. The reason why we bought all the KRW tooling at the time to do our own babbitting. So we were trying to kill the babbitt on the trip. My father drove the motor home with a tow bar just in case.
We have verified accuracy of the odometer with GPS much later because we wanted to be sure of distance. The distance of the odometer also matched the distance on the paper maps. My degree is in Physics so I like data with control to know I can trust it. Since the trip in 86 my brother has done more fuel mileage checks and it is inline.
The fuel mileage went down a bit when a rod threw the babbitt (we cant babbitt rods). He inserted a different rod and put the engine out of balance. Lost 5 MPH off the top end and the fuel mileage dropped some. Today there will be more variables to fuel mileage as formulas change based on predicted temps and state rules. They vary the additives changing the total energy available per gallon of fuel. There are also some issues with jets and amount of alcohol in the fuel.
From above: OK, two points. First, most people do not drive a Model A because it gets good mileage or worry too much about it. Second, a higher compression head will help.
The thing is items like top speed, how well it drives, and fuel mileage are all indicators of the vehicles health. If it cant do those things well it is an indication that there are problems.
Historically we know the A was able to run 60 MPH, we know it would get in the mid twenties for economy, and we know it could stop well.
How do we know, well do like I have and read all the stories on how people drove their cars back in the day when they were everyday cars. There are A LOT of stories in magazines of the day. Yes, I have read about the history. I wanted to know what I should expect from a properly restored car.
The simple truth is a car that can only do 45 MPH is not right. If the car does not feel comfortable to drive at any speed, it is not right. If it is only getting 15 MPG something is wrong.
If that is acceptable to you fine.
But maybe you should consider spending some time learning about what a properly restored car is truely able to do.
Oh, yes if you want to spend the extra bucks the higher compression head improves the efficency of the A engine. This is because today we have fuels of a higher octane that will support the compression. Back when the A was built that was a serious issue so Ford engineered the car to run on crappy fuel.