FWIW, if we did want to give Overviewer a spin for the big maps, its 1.13 format support is still a little buggy (and unreleased; I had to build from a development branch here too), but at least it renders. Also, it dropped the Google Maps API in favor of Leaflet
, a free open-source alternative. It zooms and pans and generally feels just like Google Maps. Switching to Leaflet gets around the un-free licensing problem that killed our last round of maps.
A screenshot of a somewhat old partial map backup without using our blessed texture/resource pack: