Well... if 98% sulfuric acid means 98% by mass, then that's 98g of H2SO4 per 100g H2O. 98g of H2SO4 is about 1 mol, and 100g H2O is about 0.1 L, which means that it's about 10M.
And for 500M you'd need 500 mols H2SO4 per liter of water, right? Which translates to about 49.045 kg of solid H2SO4! Seems unrealistic to me, but at the same time I can't find the solubility of solid/anhydrous H2SO4 anywhere.