yes the caps need to be align bored and yes they come in the 383/400 journal size. its not a problem to remove extra material. on most engine the #4 cap has the most stress due to its position in the firing order. that cap cracks. we use 6061 aluminum that's made in the USA for our caps. these are plenty strong and more ductile than a 7075 aluminum counterpart. feel free to call with any questions we're always available to get you some answers. sometimes out in the shop and don't hear the phone ring. so leave a message.