The HydroVac lines should be a combination of flex & hard lines. I fiddles w. a '66 in a junkyard a while back and the brake system was pretty similar to my old beast. There should be a large flex line going from your intake manifold to a fitting on the firewall where the check-valve is mounted, then a hardline down the firewall and under the truck to the HydroVac. The should be another soft line coming out of the HydroVac that goes to a small air filter, dont know where that would be mounted on your truck tho.
The inner diameter on my soft hoses is 1/2" and the hard lines are around 5/8", my rig is a bit older, but you can see the lines in
this photo as the blue flex line and the check valve and hardline on the firewall.
On your clutch issue, you should get under there and eyeball your linkage for too much play that wouldn't allow the clutch to disengage, and pull the inspection cover off the bottom of the bell housing and see if your clutch fork and throwout bearing are in working order as well. Idealy you should have enough play that the T/O bearing doesn't touch the presure plate fingers, and when the clutch is depressed you should be able to reach in the gaps in the side of the plate (assuming yours has inspection gaps/holes on the edge) and wiggle the clutch disc.
