The last time I had my 261 apart I made some measurements that showed about 4.20" between the siamesed bores (1-2, 3-4, 5-6) and about 4.38" between the non-siamesed bores (2-3, 4-5). These are at best about +/- 0.025". There was a long thread recently on the H.A.M.B (about installing various heads on a 235 or 261 to get a poor-man's 12-port) where the question of bore spacing came up frequently, but no one ever said what it was with any certainty. Many did not even seem to be aware of the siamesed bores.
Last edited by Hoyt; 12/01/08 09:12 PM. Reason: sloppy writing
