The GA bolts would basically be the fbody bolts. The fbody/C5's use smaller bolts than the GP's. That's why they bolt right up to the GA, they apparently use the same size. So even if you did use GA bolts you'd need to get sleeves to compensate for the smaller bolt. It's either that or use the stock GP bolts and drill/tap the bracket as you mentioned before. Id go with sleeves if I was doing it.