Humidity decreases the cooling efficiency of A/C but the units will remove moisture and drain it off. The max temp of any month in NH or MI is about 82 F. ....and that happens only in one month. I have 9 months over 82, four of them are over 100. Sometimes 120. You guys a lucky. Just observing benefit vs cost vs budget. Building your own will have you dizzy with all the seperate parts to buy from different sources and shipping for each. It's like building your own wiring harness, you don't save anything. (I had that itch once). Some guys will enjoy the gathering, designing, learning, customizing, upgrading....nothing wrong with that. The economy is not there. The effort is greater than a kit. IMO.
The kits have instructions!
A complete system at Old Air is $1110. They use an underdash style, looks to me like a clone of an old Mustang evaporator. Looks like a Sanden 508 compressor or clone. Includes heater function. you don't have to hook that up. A/C only kit $1035 and $1070.
Vintage Air.........has nice units.
Semi DIY option:
In my opinion the old school underdash is way more era correct for 1966. 1966 did have factory air option. Many owners bought aftermarket A/C at some point. You can buy a used genuine underdash evaporator on Ebay. Nice American made chrome ones. Selectaire is a nice "era correct" evaporator. Then obtain all the other comnponents new. Singular assemblage or kit. Which will all be R134 compatible. The evaporator will have been used with R12. It is the least critical and easiest to convert.
I have no info, good or bad, on any one source for kits or parts.
