I like the 4.00 inch stroke SB combo. At 4.125 and 4.250 you start to run into things. Oil pump, windage tray, etc. start to get in the way so the assembly just takes longer and you have to be willing to modify parts and/or buy different parts until you find a combo that works. Using the smaller Chevy rod journals sure helps. For a race engine it might be worth going with the Honda journals or something like that. I think the Hughes Engine kit uses a 4cyl rod bearing to get the size down.