There were some 70's or 80's Pontiac triangle shaped louvers that I saw here on Stangnet installed on a otherwise stock hood. I thought it looked pretty good, but everybody's tastes are different.
On covering up the holes in the engine compartment, try sheet steel, pop riveted in place. Since you need Bondo to cover the welds, use pop rivets instead. The Bondo will easily cover the rivet heads. Done correctly with enough pop rivets, it would look just as good. Even better, get out your pneumatic rivet driver and use flush rivets to hold the patchwork in place.