Started at 4 inches but with the grinding and filing for fitment..may be 4.25 inches. Used the articles from OldSkool Rodz along with the information submitted here on the h.a.m.b. There are some good folks here.....
I cut mine 5.5" and it was already channeled the width of the frame. An old van 3rd seat sat on the floor.
Suggestion? Channel (body drop) the cab 1/2 of the total chop for a realistic profile without the clique cartoony look. Still running this drive train? It looks so far like you going for a conservative hot rod back when look. And it look's fine so far.