Spelunky "Modern" was released, but installer of the "Classic" version needs few adjustments. I can easily install both games in separate folders, but both of them want to create a start menu shortcut in GOG.com\Spelunky folder under the same name.

My recommendations:
1. Change the installer's file name to setup_spelunky_classic_2.0.0.3 (or 2.0.0.4, if this will count as an upgrade)
2. Change the default installation folder from Spelunky to Spelunky Classic.
3. Change "Spelunky" to "Spelunky Classic" in start menu shortcuts.