Hammond Output Transformer Specs

Yes, the documentation is light but in this pdf there are primary impedance, secondary impedance and watts. Not enough ? and for some of them the amp where it can replace the original TR. Maybe take a look at the schematic of this amp and you will have more information.
 
But I think the above data sheet has an error with 12.5H as the primary inductance, since most of the 4K primaries are 3.5 to 4H.
Not sure what you are saying here about '4K primaries are 3.5 to 4H' ??

Are you saying you measured the P-P inductance of 50W OPT's with 4kohmPP nominal primary ratings using a 1Vrms 1kHz signal with no DC?