Some people put valves on the hoses and close it off. Check both lines from end to end. Another thing you may not be running a thermostat. Did you check that?
Don't understand the need for speed in the rain. Myself I wouldn't take a classic out in the rain....it's like thier worst enemy (rust) is encouraged. Been running BFG's and have no issues. I also have good 5 leaf springs and a 1" sway bar in the rear. I'm am adult so I drive according. I do...
I went with new springs but 1 more leaf than stock. It leveled out and had a really nice ride. Originally they sat a little lower in the rear. I hate shackles and don't like seeing them below the body.
Previously i replaced with a new hinge and it became a nightmare trying to adjust the door. Rebuilding your old ones sounds like good advice if parts are available.