The proforged tall BJs definitely use the stock style mount, I know several people that have used them and they bolt right up. Howe also makes one that works with the stock style mount but they're about twice the price of the proforged ones. I'm running the Howe's but only because the proforged ones weren't out yet when I was in the market. I run proforged tall lowers and they look like high quality pieces. I ordered my Howes from Markus at SC&C and told him that I wanted them with the stock style mount. If you're confident that the speedway arms have the stock style S10 BJ mount I'd just order the proforged ones.