In a large bowl, stir together the oil, tomato sauce, vinegar, basil, minced garlic, salt and cayenne pepper.
Add shrimp and toss to coat. Cover and refrigerate for 30 minutes (longer if desired) tossing once or twice.

 

Remove shrimp from marinade and reserve remaining marinade.

Drop whole garlic cloves in a pot of boiling water to blanch for 3 minutes.
Drain well and reserve.
Soak bamboo skewers in water for at least 15 minutes.
Peel and devein shrimp, leaving tails intact, if possible.
Thread 4 shrimp on each skewer.
If using the 12 whole cloves, put three cloves on the skewers between the shrimp.
Grill until shrimp turn pink, brushing with marinade, about 5-8 minutes total.

 

Remove shrimp from marinade.

Grill shrimp, turning once, about 2 minutes per side.

I don't bother brushing with the remaining marinade as there seems to be enough on the shrimp already.