[Hcb3200]

First note: Remember in the 55-57 series the glove box door swings down below the dash frame edge. That picture you posted will work in the center and leave clearance from the door. Some units are much longer that go under the dash and hang down and glove box door was issue. If you are redoing your dash to smooth and removing door its not issue. Some units go behind the glove box you loose a lot of storage with those in glove box. your truck decide how you want to do it.

Second point; Make mockups. all the sites have dimensions cut you some cardboard boxes down and make some mockups to move around and see how much clearance you have or how low it goes etc. if you are near some speed shops or custom shops some even have plastic mockups from vendor go try them out before you buy the real thing etc.

Most 55-59 have defrost vents in place and plenty of room for flex tubing to get back there. just make sure its out of way of wiper transmission when running.

As to are they any good. i have a mix and match of stuff from multiple places, condenser, dryer, mounts for compressor, hoses (custom made by me crimped at local shop) etc. evaporator from generic vendor etc. and i am frozen out of my truck if i leave it on high and plenty of warm and defrosting in summer. Make sure whatever you buy has the extra defrost ports out. some heat/ac systems don't have defrost.