Um, k...tips on getting your lower chest to look like Arnold's:
1. Acquire his godly genetics.
2. Use gear.
3. Get to his level of mass. If you want a chest like Arnold's, you're probably going to have to have a back like his too. And have you seen that fucker?
Before you worry about trying to add mass to your "lower chest," how bout you worry about adding mass to your entire body, everywhere? Your chest shape is genetically determined.
Do you already bench 300-400 pounds for reps? If you get there, whaddya know, I'll bet your chest will get a lot bigger.