You can see depictions of the Euro and EPA exhaust system configurations at www.timevalve.com
I won't sermon you on emissions requirements but other federalization changes can include US spec bumpers, sealed beam headlights, US spec front corner lamp sockets so they're side markers as well as turn signals, US spec taillights with a red strip on the leading edge, addition of door side intrusion beams, mph speedometer, unleaded fuel filler restrictor, maybe fitting a US spec headlight switch that only allow fogs with the low beams.
Comparing numbers, a Euro 500SEL has 8.8:1 compression and goes 0-100km/h in 7.7sec. A US 500SEL has 8.0:1 compression and goes 0-60mph in 9.0sec. I think the cams are the only other major internal difference between Euro and US spec cars.
As I understand all Euro V8 engines have double row timing chains. Only the early M116 (380SE/SEL) had single row chains. Your car has an M117.
A Euro car should be considerably more powerful but who knows exactly what was done to federalize and California-ize it plus what's been done to it in the last 20 years.
I'm sure many parts are shared between the Euro 83 and US 84. Your best bet is to consult Phil through the PartsShop link at the top of this page.
If your car has rotary knobs to control the AC I hate you