Wolf, don't know about the fuel tank issue, but the fuel hose (stock) in the engine compartment is a metric hose, but as you've found the 5/16 in. stuff seems to work fine. I've also replaced that two sized hose coming out of the tank. I tried to stretch a hose, use a step up adapter tube and hose, but finally gave up and ordered the correct part. I think this is a must on that issue. If you ever have to replace the vacuum pump hose to the brake booster, then you'll have a little more problem. That stuff has to be heated to remove and install. I couldn't find any so I first tried Apex plastic (I think) plumbing tubing. It worked, but I didn't like it and eventually changed over to plain old good quality rubber hose. I am happy with this arrangement and it looks a little better than the Apex stuff. Also rebuilt the vacuum pump. The other good one is the pre-shaped plastic oil return hose from the cam housing to the top of the oil pan on the driver's side under the intake manifold. Have you had the pleasure of replacing that one? I just did it a couple weeks ago, and got rid of my last oil leak....cheers!!