Does anyone know where I can find an absolutely reliable and comprehensive guide or chart so that I can take my AGW20H 93851-6064 and determine precisely what other blocks I can use in its place. I need two of these and I may not be able to find that exact block. And that's fine. But I can't afford to order some other brand of 20mm block and then find that it won't fit my rails. Any help will be appreciated.