I just went through the fuel line swap in my van.  It is sensible to eliminate the plastic wall fitting and just run high pressure line hose through the firewall.  The grommets that positing the air cleaner holes are perfect for the firewall hole and you can get them from busdepot!  There is one problem though, tjust before passing through the firewall the line comes into contact with a cooling line.  The stock plastic tube had piece of asbestine cloth over it.  This is a necessary mod!

Hopefully, one less flaming vanagon!

Jeff