"if keeping the car" should it be.
3rd digit in your VIN is a letter that designates the body style. If unsure of where to find your VIN # click on this help page link: www.vin.6364cadillac.com. If letter is K (i.e. VIN 63K......) you have a Six Window Series 62 Sedan. If letter is L (i.e. VIN 63L......) you have a Six Window Sedan de Ville.
As far as difference between Series 62 and deVilles most differences are in the interior and options vs standard equipment.
On the exterior you will have a Sedan de Ville script on the rear qtr panel; on the Series 62 no script on rear qtr
On the interior, styling is completely different. For deVilles you will have a full arm rest on the door that integrates the arm rest and switch panel, and includes the power seat switches; Series 62 has smaller switch pods in front of arm rest and power seat (if equipped) switches are on the lower metal trim base of the seats. De Villes have courtesy lights built into the doors; series 62 has non-lighted reflectors. De Villes come standard with power seats and power windows; series 62 do not. 1963 Series 62 has vertical pleating on the seat bolsters; deVilles have a squared pattern with buttons. The deVilles have a front center arm rest, while the Series 62 do not. The materals used were also different. I could go on and on but the dealer data book scans below will give you a better understand of the differences.
Series 62 Six Window Sedan:
Sedan de Ville Six Window: