I want to run new gas line to an upstairs dryer and the county inspector suggests using black pipe. I've priced all the fittings and nailing plates and it seems like the stainless steel is going to be more expensive. My brother in law (a pipefitter, not a plumber) will help me with the work. He says that using the black pipe, I won't need to use a manifold or the inside "pounds to inches" Maxitrol 325-3 regulator that was part of the flexible yellow copper line I want to replace. I have a 2lbs of service at the meter. Is he correct?

I don't know anything about manifolds or regulators but do know that many local codes no longer allow flexible gas lines and yes, black pipe is the way to go (with a valve reachable for shut off and easy removal while dryer in place).

I assume, Black Pipe is rigid steel pipe that you buy in 21' lengths and process it on the job site ? Correct ? This pipe you have to cut and thread. It is the old-fashioned way - but probably the best type - of installation.

For gas dryer ( 15,000 to 18,000 Btu's ) you will need 1/2" gas pipe.

You can use Trac Pipe (yellow) gas pipe. It is flexible corrugated stainless steel pipe that sells in 100' lengths.

Last night I wasn't very clear about my problem. I emailed Maxitrol today "I'm doing a major renovation to my house and decided to replace the yellow flexible copper with traditional black pipe. I have a meter rated for 2 psi and have 2 psi at the dryer (where I had the pressure gauge set for my municipal building inspector to see that the new lines hold 15 psi). In the old configuration, there was a manifold connecting a line to each appliance (water heater, furnace, etc) with a Maxitrol 325-3 connected at the start of the manifold (line coming from the meter).
My plumber says with black pipe, this pounds to inches regulator isn't needed. That each appliance has it's own regulator. He's great but he doesn't
work with gas often.
Is he correct? I don't want to blow up my house (or me)."

Maxitrol replied " Your appliances' regulators are not rated for 2 psi supply pressures. You still need the regulator to bring the 2 psi supply down to appliance level pressure.
You should contact a certified and licensed gas fitter to consult your home's gas needs."

So they say I do need a regulator inside the house to bring down the 2 psi at the meter to the correct pressure for the appliances.
The old 325-5 is 1/2" but my new line is 1". Should I buy a new 1" regulator or use adapters with the old one?

Usually, gas meter has its own regulator located on the left side of the meter. This regulator is owned by the City. With that regulator present, you usually don't need any other gas pressure reducing device.

However, some stoves and cook tops manufacturers supply additional gas regulators that install right at the oven / cook top. This regulator helps to equalize pressure fluctuations within the already reduced pressure past your gas meter giving you nice, steady and continuous flame at the burners.

Do you have pressure regulator at the gas meter ?

Yes, it's marked Schlumberger and has a yellow sticker attached "Natural gas, 2 psig line presuure". I don't know what the psi is coming to the meter, but it's 2 psi out and into my house.