Lumen you're not the only one that's struggled but I'm just about there. It was only when I got the theme (and from that the location) I realised they were different extra letters for 1ac and 1dn. Glad you got there.
Many of the clues really tough and quite a few I only got because of getting the theme or the hints on here (like 39d - thanks primeprospect). Still not sure of the wordplay on some.
Hardly any familiar words in the grid. Even then like 40ac, it's the most obscure definition possible.
Unfairest clue competition: 24dn - surely fairer to give us what sort of species rather than the year it died out. Were we supposed to go through hundreds/thousands of gods till we found a heartless one that gave an extinct species or find a list of extinct species by year?
Enjoy a challenge but hoping for something just a little easier next time.