If you get anxious, and farm some "shopwork" out, don't forget about Andre's shop tools at River Leaf Models.( His 1:48 operating bench vice comes to mind everytime I look at one of mine)
HVAC; while newer ones are more similar to each other and many much smaller than they used to be; the older, the more imagination you can use...talk about variation! Everthing had more style years ago, even hvac 😄 On a modern one, an open panel with a keyboard& computer screen running Linux wouldn't be beyond you 
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The best choice of system size itself taylored to the space inside, expected air travel and operation costs are a science in themselves anymore. Older systems often began with an office or two with other units being added much later to expand the treated area. Large and high traffic buildings go sar far as to read air pressure drops when specific doors open and compesate in an effient manner. That ability may or may not have heat/cool ability and may be integrated or a stand alone unit. ...bla bla bla... You can ask, but the sky is the limit on a big box with vents I've replaced "bomber propellers", installed "indoor Pacifics" and worked larger , improved paintbooth filter and flow for RR shops in 1:1 scale, piped diesels exhaust away from our First Responders vehicles and worked in the one of the best air scrubbers any surgery wing ever had. But nothing beat running in a 12foot squirrel cage fan because I could 😁... 🐿️🥜🍨. 🤔🗓️..😜
