body drop questions, please help!

I am debating a 3 inch body drop, my truck is juiced notched lowered control arms etc. Etc. It already lays frame on 16 inch hummer h3 wheels. I want to lay rockers on 20 or 22 inch wheels. Any advice on how to accomplish this would be greatly appreciated, especially advice on retaining factory heat and ac! It's an x cab 2600 automatic already converted to carb if any of that matters thanks!!

Factory heat sucks. Get vintage air if u want heat and a/c

What?!
My heaters will run you out!