On my 73 I left the steel line in place by the frame below the master cylinder and then took a short piece of tubing and pushed it onto the steel line and then pushed on a PCV valve onto the end of the rubber line. My thinking (and it's worked this way for many years) is that the PCV valve will let air into the tank but if fuel fumes come forward up the line the PCV valve will close. I can't remember if I used any type of clamps but adding them wouldn't hurt.
I'm also working on an El Camino for a customer at the house and they added a sump to the tank and someone else capped both the original vent line and fuel line off of the top of the tank and when I went to drain the tank using the sump fittings the fuel ran out a while and then you could hear air rushing back in stopping fuel from coming out and then some more fuel would start coming out only to stop once again whil the tank gulped in some more air. I dropped the tank and since the old lines running forward were not going to be used I bought a 2' section of 5/16" fuel line, some worm clamps, an Adel clamp, and a PCV valve and then put the new line on the tank vent line and routed it to where the Adel clamp would secure the PVC valve to the underside of the floor pan on the gas tank support bracing.
If you are working on the car you might want to check the other rubber jumper connection hoses on the car. The original ones are probably shot. I would also use the worm clamps and use those instead of the original spring style clamps.