>I remember reading an article in GM High Tech Performance magazine that had the part #'s for the fuel rails to allow going bigger from the stock size to a larger size (maybe) an -4 or -6.
I don't really remember, but would like more info if anyone has it.
this isn't for the rail itself, but for the connectors.

 

The stock fuel supply line is 3/8", which is equivalent to -6AN. The stock return line is 5/16". There is no AN equivalent, so you need to use -6AN for the return as well. I use -6AN supply and return lines to support 800 flywheel HP, so you shouldn't need anything larger.

Look at an Earls catalog for a 3/8" compression X -6AN fitting to convert the stock supply hard line, and a 5/16" compression X -6AN fitting to convert the stock return hard line.

 

>Thanks Fred
I do remember something about a "kit" maybe from Horse Power Tv... but anyway they used the original LT1 fuel rail (where the injectors connect) and welded an AN -? fitting and also included the female AN -? side too.