Sorry for my late reply due to the moving of my company.
To my knowledge, the SRO speakers were built with ALNICO magnet and with basket of SP series and were discontinued in the early 70's when E-V launched their new range with new basket and ceramic magnet like EVM, FORCE and DL series, SP12C and SP15A speakers. Beside these new models were supplied with data sheet showing the newly introduced T/S parameters.
So in a nutshell, we don't have any data sheet showing the T/S parameters of SROs and as I exposed elsewhere in the forum these 30 years old speakers should be measured to get useable T/S parameters because of ageing of the magnet, suspension, etc. Nevertheless, these outstanding speakers remain really worth to be used.
I have some short info concernig SROs somewhere. I will post them to you asap.
Best regards,
ERIC