I'm at that stage in my current build....removed the heater...I use a small portable 12v ceramic heater when it gets THAT cold....the A/C is much more critical. I've installed underdash A/C only, units before....check yellow pages for auto air suppliers. Our local supplier carries all the parts and is more than happy to help match up the system. Even crimpes my hoses for free after I get everything set up. A/C is simple and trouble-free, until you start adding solenoids and other do-dads that just cause you problems.
I've checked on several packages...all have features and little quirks that I didn't like, or need....and rarely offer the brackets and pulleys that are critical for the install. My total for installs is usually $300-$400 less than the so-called complete packages and I can mount the compressor and run the hoses where I wanted them. Hope this helps.