Using a GDA before your preworkout meal is a great time. For me personally, I prefer to take a GDA 15-20 minutes before a moderate to high carb meal, let that digest for about an hour, and then train. Pumps will be epic.
Na-r-ala and agmatine are both great ingredients to use as standalone, but you could also check out a more complete nutrient partitioning product like Slinmax. Slinmax contains both of these ingredients along with some others that can help with digestion and blood sugar control