besides the staggered and step hull is there any size difference between an older fountain lightenin like a 1991 to a newer one like a 2007 as far as height, length, width, etc

What size boat are you talking about? By 1991 I am pretty sure they incorporated the swim platform into the model size so for the most part they should be the same.

sorry 42 foot

A 1991 42 Fountain should be the same size as a brand new 42 Ex. Like you said the newer boats have steps and staggered engines but all the overall dimensions are pretty much the same.