I know little about AC units, but the pic of the front unit mounting worries me. I don't see drilling/anchoring into the end grain of the 2x's as being the ideal way of attachment. If possible I would use metal, and if wood is the only option, then perhaps cutting NEW blocks that allow attachment/anchoring on the edge of the 2x, as to allow the screws to grip the grain of the wood.
This is an interesting question. There are 3 screws going into the frame are at a 45 degree angle which cross the grains. Two which you can see in the picture and one on the bottom of each bracket. My concern with the grains going the other way was if the screws going vertically up from the bottom (to hold the bottom wood facing in place)would split the wood over time with the vertical forces (bus bouncing up and down) and the whole front could possibly come off as opposed to a horizontal split in the wood where another screw would still be able to hold the weight of the evaporator with the up and down motion of the bus. Makes you scratch your head and think about it...which I did for a bit before making a decision. Again - Metal would be the best solution and in the future when I have time, I might take this apart and weld something in.
Let me know what you think.