Everything I've read advises against boring out the 413 block to 426 due to cylinder wall thickness issues. I would stick with the 5697 block. Physically, if you are using MW size valves, you will need to notch the block. Some builders like to do it anyway to unshroud the valves and improve flow through the cylinder. It also gives you more head and valve options if you decide to go with something different later. My 2 cents YMMV. _________________________________________________________________ Need to know now? Get instant answers with Windows Live Messenger. http://www.windowslive.com/messenger/connect_your_way.html?ocid=TXT_TAGLM_WL_messenger_072008 -- [Non-text portions of this message have been removed] ---- Please address private mail -- mail of interest to only one person -- directly to that person. I.e., send parts/car transactions and negotiations as well as other personal messages only to the intended recipient, not to the Clubhouse public address. This practice will protect your privacy, reduce the total volume of mail and fine tune the content signal to Mopar topic. Thanks! '62 to '65 Mopar Clubhouse Discussion Guidelines: http://www.1962to1965mopar.ornocar.org/mletiq.html.