ok so im kind of lost because i cant find anything on it. yes i searched so here is my questions or possible solutions. the 305tbi is a return style and the ls1 that i have is a 2000 none return style. so 1 solution get a 98 vette rail that is a return style system and weld on some an fittings and run the lines one from the fuel pressure regulator to the rail and the other from the rail to the stock return line. is this possible? or should i stick with the 2000 none return style weld a AN fitting on it. run the stock lines to the fuel pressure regulator feed and return lines and have one going to the fuel rail. which one seems like it would be a better idea? also is the correct AN size -8? i dont know what my stock line from the tank to the fuel pressure regulator is but from the regulator to the rail it will be like 1/2 inch? not to sure. this is my only concern at this time i pretty much have everything else mentally figured out.

I don't think you can use the stock TBI lines. TBI runs at a much lower pressure than a MPFI system found on the LS1. I have FAST fuel rails and an aeromotive AFPR for my genIII project.

what air fuel pressure regulator do you have?

Use the return style system.

Here is why: The later systems (returnless) are designed to pressurize the system from the tank forward with a variable pump. You don't need to re-engineer you whole system since you want to essentially "recycle" the hard fuel lines between the tank and the block. You'll just give yourself a headache if you try to go returnless.

You'll have to get a pump with more punch, adapt the lines in the front to the new rail, AND use an LS1 FPR on the rail.

As for AN conversions...

3/8s ~ -6AN
5/16 ~ -5AN

Here-
http://www.holley.com/types.asp?type=223

Hope that helps!

I orderd a areomotive pn 027-13109 from jegs

AFPR=adjustable fuel pressure regulator