Just try inserting a hose from aft and go forward.... I guess you want to drill holes in front of rails ?
I used the existing holes on top of rails....
There is a hole in the very rear most portion where the frame rail intersects the cross member under the car. I pushed the fuel line in through there, I'm using hard line, not hose, because most racing organizations frown on extensive use of rubber hose, and I'm not willing to buy 20 feet of braided steel, which will fail within a decade anyway. There are a few holes here and there along the frame rail where I was able to view tube progress into the frame rail. The line was moving forward successfully, albeit with some manipulation, right until it came to the rear most K frame bolt, where it stopped hard.
There is a small hole in the top of the frame rail on the front side of the shock tower that I was trying to get the line to so I could then screw in the line adapter, so I was stopped about 2" short of where I need to be. After that, I did try feeling around inside the rail, which is not easy because the hole in the rail is only about 1" diameter, and sure as $h!t, there is a plate in there. It also feels like there may be a small square pass through in it, but too small and not easy to hit when you're manipulating a line from three feet away that is curving up the inside of the rail (its not a straight shot by any means).
Looking at the side of the frame rail in this location, I can identify 4 factory spot welds here, as well as similar welds by the front K frame mount. Peering in the front of the frame rail behind the bumper and through some other various holes, I can see the front most bulkhead, so I know they are in there.
Then again, my car is a late '74 build, so maybe these are updates to the frame that weren't in earlier models. I'd also be in the clear running anything in the rail up to the shock tower. Anything in front of it will present a difficulty, so I suppose I could move my fuel regulator behind the shock tower and reverse all my fuel log set up. Of course, this will fight for space with the heater control valve and associated heater hoses, so its going to make that corner of the engine bay somewhat cluttered, which is what I'm trying to avoid overall.
On a separate topic, Anyone tried putting a water temp sensor into a head casting plug instead of the intake?