2500s in front

ive got a 350 in my isuzu. everyone has told me i need to run a 2600 in front but i dont see how the hell its goin to fit in there. anyways i was at dragfest today and a guy was up there with an older fullsize that had 2500s in front. got plenty of lift for me. so my question is if u can use a 2500 on a fullsize with a small block why does everyone say i need a 2600 on my mini.