Steam Heater Help

I'm fairly new to this steam stuff and being in down in south texas we don't have much of it.  Came across a problem and hoping somebody can help me out.  I have 4 steam heaters we have to replace in a warehouse that are probably older than I am.  The only info I can find on them is "National - U.S.,  model no: 74-B14CK3Z6AG, serial no: Y1982HH, Crane Co.  1 1/2" inlet and outlet.  I can't find any specs on it anywhere online or through our local heating companies.  Basically its a big radiator that steams runs through with a little blower on the back side.  I have talked to everybody I can think of trying to find a suitable replacement for all 4 of them with no luck.  Any help would be much appreciated.  Thanks.