To the best of my knowledge, no Deville has ever been equipped with a V6. The earliest that I know Devilles have been around is the 50's, and they all had V8's. Through the 60's and 70's they had all big-block V8's, the largest of which was 500 cubic inches. At some point, either late 70's or early 80's they switched to small blocks. By the mid 80's they were using a 4.1 liter small block, which was increased to 4.5 liters in 1988, and then 4.9 liters in 1991. Mid 90's they came out with the Northstar V8, which has remained largely unchanged, and is still being used in the Devilles now.
The 1992 Cadillac Deville came stock with a 4.9L, V-8 engine with 200 HP.
The Deville was only available in the coupe and had a 454 or a 455 V-8. The Eldorado was a convertible and only had a 390 V-8.
You can find a 2003 Cadillac V-6 engine cooling system schematic diagram at most Cadillac dealerships. Many auto-parts stores will have the cooling system diagram.
The firing order for a 1997 Cadillac Deville is 1, 2, 7, 3, 4, 5, 6, 8. This is for the 4.6 Liter engine.
The 2004 Cadillac CTS-V has a V8 engine.
The 2007 Cadillac CTS-V has a V8 engine.
The 2009 Cadillac CTS-V has a V8 engine.
The 2014 Cadillac CTS-V has a V8 engine.
The 2011 Cadillac CTS-V has a V8 engine.
The 2010 Cadillac CTS-V has a V8 engine.
The 2013 Cadillac CTS-V has a V8 engine.
The 2006 Cadillac CTS-V has a V8 engine.