The current ratings are for continuous use. I drew more like 800mA from one but that might be the 'IVS" rating for ssb.
Old iron!! Still you got a nice transformer there! It is listed in the catalogs on bunkerofdoom. I believe it is equivalent to the the P-9920 and cost $107 in 1948, $229 in 1955 with the warning 'part number to be removed from next catalog'. Farewell WWII iron design.
There is even a picture here:
http://bunkerofdoom.com/xfm/STANCOR_140H_MAY1948_WEB/011.jpgNote the official rating at 2500VDC output is 350mA CCS / 450mA ICAS, and at 2000VDC it is 500mA CCS and 625mA ICAS. So there is plenty of headroom as long as it is not abused.