How accessible do you want the valve stems? Route into the trunk or behind the rear license plate (my recommendation). May need to make a little bracket and be sure to position so it is fairly easy to get an air chuck or pressure gauge on the valves.
The rear bumper on my 68 had two unused holes behind the tag, one on each side. Perfect for the air valves and they were the right size, too.
But if you really want to try them I always used zip ties along the brake line, then up to the fuel tank bolts then over to the holes in the frame there by the tank then thru the rail and into the 2 vacant holes in the bottom of the bumper on each side
I have one in the right rear of one of my cars. I routed the line over to the rear frame rail,and there was a hole on the bottom side for the valve to mount. It faces down,and is easy to access behind/under the car.
I did what hugger suggested, ran the lines individually back on each frame rail to the unused holes in the bumper under the light assembly. They point down and easy access.
