Thanks, but not gifted at all, more "cursed" by persistent doggedness :)
Another Next Step to consider is the analysis of historical proxy records that have been calibrated to ENSO. One of the lead researchers on this is Kim Cobb from Georgia Tech, who several years ago analyzed old-growth coral from Palmyra Island in the equatorial Pacific. She discovered after correlating the isotopic oxygen content of the newer-growth coral against recent SST records that one can calibrate the two and thus the O content would make a suitable ENSO proxy record going back in time.
What I tried to do with the Palmyra proxy results is see if I could use my sloshing-derived equations to model the data with approximately the same parameters that I have been using for my SOI fit. This is the result of that, which I finished a couple of weeks ago.
The filtering is somewhat tricky because there is both a seasonal signal and a longer-term PDO-like trend riding along with the data. But otherwise, I was surprised by how much the records from hundreds of years ago match in form to what is being measured now. It shows perhaps how stationary the ENSO time series is over many centuries.
All of the data is available from that first NOAA link in case someone wants to look at it.