Exhaust manifold and waste gate flange fitment issues

[speedgod^s13]

I bought a Full-Race pro street gen 1 exhaust manifold a long time ago. The sale also included an old Tial V44 wastegate. I decided to run a new wastegate, so I purchased this one: https://www.realstreetperformance.co...o085-1500.html
thinking that it would clamp right up. Went down to the shop after it arrived, and the wastegate flange is way bigger than the exhaust flange. The manifold flange is approximately 2.5" and the wastegate flange is approximately 2". So, what are my options? Also, here's a follow-up question. When wastegates are sold, they always list the valve size, but I have not seen any specify the flange size. Why is that? Any help is appreciated.