well nascar dictates the maximum bore (4.185) which is to say you can run a smaller bore if desired you just have to compensate the stroke to meet the other rule of 358 max cubic inches. different bore and stroke combos can create different charracteristics in an engine, believe it or not maximum hp is often sacrafised for an engine that is easily driveable, like when your at a short track driveability wins races.

4/7 swap,........yup wish it was legal in nascar. well we have adapted very well without but with 5&7 fireing back to back it makes exhaust scavenging a little tricky or lets say you pay a little closer attention. for an engine if you can keep the fire cycle from fireing on top of it self then it makes for a smoother running engine.

what i dont know, is if the computer needs to be worked on to make the 4/7 work.