Vintage,
I used the stock s10 filler neck and it is flush with the bedside. I cut the neck down to where it was basically straight. I cant remember but I think it was about 7-8 inches long. I shaved off the small vent tube, thats one of the reasons that I keep the vent line out of the tank. I keep the stock triangle base plate on the neck. I was going to tack weld that plate to the back side of the bedside, but I didnt need to once the grommet was in. I doesnt budge at all. I bought a new piece of rubber fuel neck and connected it between the tank and the neck. With the fuel cap srcewed in, its flush. The cap is from a harley davidson, part number 61102-83C. Here is the website I got the grommet from. It has a really good description on how to choose the one for your specific use. I ordered a few diffferent sizes to make sure I got a really tight fit.
http://www.rubbergrommets.com/produc...oduct=grommets
The neck is tipped up about 2 degrees to ensure the fuel will flow properly. I have a bunch of pix if you need more. There a few other pix of the neck setup on my thread on previous pages. Hope this helps....let me know if you need anything else.