I have a pair of 65 289 heads, they're early heads with no thermactor. I have a friend at machine shop who is doing all my machine work for next to nothing. With valves and springs, threaded rocker studs, and completely rebuilt I'm only paying $300. So it's a good deal. I want to put 351 windsor valves in them. My guy told me that factory 351 valves are longer than the stock 289''s. I tried to research it, and it seems like 289 is 5.03 and 351 is 5.075. Between adjustable rockers and playing with push rod length should it be an issue?