What are the performance goals? The Hipo manifolds should (??) fit the 351 and will take less modification than long tubes. Good compromise between stock log style units and tubular. If you want max power, though, you can't beat long tubes and the '69 body has room. I tried SuperComps in my '65 and even the muffler shop could get 'em in. The repop Hipos fit just fine. Just a thought.