I bought an 8000 BTU air conditioner off Facebook Marketplace for $20, so of course it didn’t come with any mounting bits. While I had an external mounting brace to support the hung weight of this big machine, the brace made the A/C unit rest high on the very narrow middle part of the brace (i.e. it was wobbly). So I made some bits to better support the A/C unit body and keep the window from opening.
The bottom support blocks have a cutout to follow the slope of the moulding common to new construction. The negative space is also present in the model so you can hack it to your needs. The window stop caps mate with 1/2 inch dowel rod, and shoving a little “caulk-saver” foam inside the cap acts as a nice spring to make inserting/removing the window stop easy.