You can put 351 W headers on a 289 but on a 351w the headers bolt to the heads at a higher position because the engine is taller than a 289. If you bolt them onto a 289 they will be sitting lower than they were made to. They might bottom out. But again, you can get them easily modified by taking them to a shop, lifting the car with 289 up, install the 351 headers and have them heat the pipes and bend them to form better to fit. Or you can do it yourself. I see you are in the bay area CA. Me too. In Pleasington or something like that there is a swap meet/car show this weekend March 24 & 25. You can pick up a used set of 289/302 headers that fit correctly from $25-100 depending on the condition. Or you can call Mustangs Plus and ask them to bring a new set to the swap meet for you. They charge you the catalog price, no shipping and no tax. They have a wide variety to choose from. Tri-Y's are good and bolt in no hassels, about $140.