One pipe steam????

Oh yes they do, you probably don't know they are there.

Look at the upper pipe tapping on the side of the rad opposite the supply valve. You might see what looks like a plug, but I'll bet there's an air vent in there. It's called the "In-Airid" and was made by the American Radiator Co. Here's a scan of the In-Airid section of the 1929 Ideal Fitter catalog.

Here's what I'd do: After a visual inspection and a successful test of all the safety valves and controls, fill the boiler in the usual manner. If it doesn't leak and you determine the boiler is safe to operate, you can fire it up, but be ready to shut it down immediately if required. I'd have several guys in different parts of the house and another at the circuit breaker panel to make this happen. Start firing for short periods and don't let pressure build up right away. Sometimes only a slight pressure will reveal a leak.

There's always some uncertainty when starting a boiler that has not been used for some years, but with reasonable care you should be able to handle it safely. But I must admit I've never actually done this- if anyone out there has more suggestions I'd like to read them too.

If the boiler is really that old, I'd consider just replacing it.