Some say the cylinder walls are shorter in 289 blocks but it's one of those "Internet mysteries". Only thing I saw consistently was 347 strokers "push" it so that's why I went 331. Also the stroke ratio is better on the 331 for quicker revs. Bore is the exact same on either block, 4.00. Bor on mine is 4.030, stroke is 3.25. 5 cc valve reliefs, 60 cc chamber, 1.6 ratio, .500 lift, 10.1 compression.