What motor?
Vintage Air is the company that has been around for the longest; they had a street legal Stude that ran over 200 MPH at Bonneville with the A/C on! There are a bunch of copycats and a couple others that do nice stuff. If rodder type A/C is what you want, check them and the others. See if anyone has a custom-fit for your application, and use that to compare the others.
If you want the resto crowd vintage aftermarket (dealer-installed) type, it will be harder.
Go down to the local news stand and pick up a Street Rodder and a Hemmings (the big thick one, not the pretty pictures one). That should give you a shopping list.