One option is you can order this mock-up version of the Gen IV to test fit it in place of the original heater unit in your '63 before ordering the actual evaporator. I used the Gen IV in my '68 Barracuda convertible and bought the underhood stuff from Nostalgic AC Parts in Florida. I used a much larger condenser than Vintage offered.

https://www.vintageair.com/custom/product-pop.php?pn=671450

https://nostalgicac.com/

Don't forget to insulate as much of the interior as you can while you have it apart. Dynamat dampens the panel resonation, but its the double-sided, foil-covered jute mat and aluminum foil duct tape combo that really stops the heat, sound and fumes from passing into the passenger compartment. Grab that from Speedway Motors.

https://www.speedwaymotors.com/Aluminized-Heat-and-Noise-Insulation-Shield-Double-Sided,32193.html