Here is the stock filler neck, cut-down. Notice the fuel nozzle stop. You want to retain this.
So there you have it. Your filler neck / tank connection will vary depending on application
Above: I began welding in the rear wheel wells in, permanentley. The passenger side was easy, the driver's side wasn't. I had to figure out a way to feed the gas tank from the stock Merc filler inlet in the quarter to the vertical Lincoln fuel tank. A soulution came in the form of a steel "donut" obtained from a sand rail site on the 'net. I paid $30 bucks for a  complete 360 degree circle of welded 2" tubing. Using this, I determined that I could weld up a fuel filler neck that would extend some 20 inches from inlet to stock 1988 Lincoln tank, all on a downward slope. It might take a while to fill the tank, but hell, this car isn't going to be in a rush to go anywhere...
Above: You can see in this shot, the driver's side inner wheelwell/trunk area. It's pretty straightforward; find a piece of  sheetmetal, contour it to fit, and weld it in. I had to torch and beat on the yellow areas to mate them to my 90 degree floor add-ons as the '51 Mercury bowed in this area; and I made my patches fit to this contour.

You can see where I cut a square hole in the fenderwell to allow for placement of the filler neck. I plan to use the original 1951 Mercury filler "funnel" and rubber gromment to intersect this area and keep the road debris/water out. The main problem with welding in a solid "pipe" to go from the filler inlet to the tank is that you won't be able to easily remove the tank once it's all welded in, because of the contours. I have elected to create the shape needed to mate the inlet to the tank, and then use a section of fuel-proof rubber hose (similar to the arrangement used on '63-'64 Impalas) in order to be able to remove the tank/fine tune the placement. It will be a 2" section of rubber fuel proof hose in line with the fuiller neck..

Below: The rear frame rails kicked up too much before exiting the stock Merc body. the only solution was to cut off the excess (which I did way back when I was trial fitiing the body), and then pie-cut the stub to get it to come back in line with the rear-end end end of the Merc. If i do this right, I'll be able to cut-and-paste in the stock Lincoln rear frame; the stock Merc body mount locations are pretty damn close. I have a set of "universal" poly body mounts I got from Summit, so the next step is to figure out how low the frame needs to be re-welded...and how it will line up with the stock rear body-busings on the Merc trunk floor. Shouldn't be too much work.
Above: This is the v-notched frame, angling it more downward than stock so I can adapt the Lincoln frame to the Merc body...
I V-notched the frame and bent it into submission. I re-welded in the original V-shaped chunk back in. The little Lincoln 135 MIG welder that I have workerd really well on higher settings...even for a 110. The joint is very strong.

After I did this I lined up the remaning 1988 Lincoln rear frame. With some tweaking, I can get it to work with the stock 1951 Merc body mount locations.

The Energy Suspension polyurethane body mounts seem to be the ticket. I'll post pics when I get to that part...and if they work okay, I'll use a similar setup on my core support; which I have to fab from scratch...
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