Answered Revolution Templates on Evolution?

Main differences will be tagging syntax and extra/plugin compatibilities. This should help: http://rtfm.modx.com/revolution/2.x/making-sites-with-modx/tag-syntax

Other than simple tag syntax you'll need to make sure you've created any custom template variables the new template may require (unlikely if it's a generic template, but possible) and you'll need to be sure you have a working Evolution version of any snippet the template may require, like Wayfinder for menus.

One big gotcha would be if your template incorporates any getResources calls, in which case you would have to rework that area to use the old Ditto snippet for Evolution.

Really depends on the complexity of the template, but it shouldn't be too difficult.