Width of firewall on Kitfox 5 to 7 needed

[1avidflyer 1983]

Hi all,  I'm trying to find out what the width of a Kitfox 5, 6 or 7 is.  I have a smooth cowl for one of them, and want to modify it to fit a Kitfox 4.  Thinking about cutting out a wedge shaped piece to make the back part of the cowl narrower to fit the Kitfox 4.  Can anyone grab a tape measure and measure the firewall at it's widest place?  Thanks,  Jim Chuk