I'm preparing to finish my walkout basement. All basement has drywalls just the external wall not. Basement has no water problems (the house is on hill and the balcony is above the wall that I want to work on) and is relatively warm also all wall is painted.The problem is that the wall is uneven. I want to use rigid foam and 1x3 attached right to the wall, but the upper part is disaster. Not just different uneven, but different material too (concrete and probably dry wall or wood). Because it's not a big surface I want to level the wall's upper part with some wood shims (pieces of 2x2 or 1x3) and use can spray foam to fill into empty spaces between the rigid foam and the wall. Does it sound totally stupid or it's possibility? here are a few pic for more visuals. Will be very thankful for any advice.