Yes. The engines are both V8 northstar engines, the one in the SLS is just a different version with less horsepower and more torque.
How to Replace spark plugs on 2004 cadillac deville Sls with 4.6 v8 engine
There may be other differences, but the one I know is the SLS has a 275 HP engine and the STS has a 300 HP engine.
yes 20's will fit fine with no lift kit or spacers
Yes, it's the same size engine the sts just makes more hp(300) then the sls(270) engine, should drop right it
on the right side of the engine at the top its on a separate belt
It is located underneath the engine, near the intake manifold. The engine will have to be lifted up for it to be removed.
16.7 feet or 200.9inchs
7 qts for the 4.6 L Northstar engine
assuming it's a Northstar engine. It's in the center of the engine below the intake plenum chamber.
Northstar engine is rated at either 280 for the SLS or 300 for the STS for 1999.
2003
You can purchase a Cadillac SLS from auction websites such as eBay motors. Alternatively, you can purchase these vehicles from classifieds such as Craigslist.