1) I'd first make sure the oil is leaking from between the junction block and the engine block, not the oil pressure light switch or the hose. Yes, if that hose breaks you will lose oil pressure, all the oil within about 20 or 30 seconds, and generate a very impressive cloud of smoke as 4 quarts of oil spray onto a hot exhaust manifold. Use teflon tape to put the fitting back on. The threads in the steel block are almost certainly not damaged, but they might be trashed on the soft brass block - you could probably replace it with some plumbing fitting - take the old one to a hardware store and poke around.

2) On a '66 it should have the 'backwards' gauge - seems to work backwards of everyone's intuition and almost every other gauge. It uses two duelling magnetic fields to point the needle. One comes on when the ignition is turned on - 12 V to one side of the gauge, grounding theough the gauge body. This pops the gauge to a full reading. The other field is powered by the same 12 volts, but grounds through the tank sender - it pulls the other way, and when fully grounded by the sender it should read empty.

3) Stumbling around corners - could be an off fuel bowl level in the Weber. And the Webers can be more sensitive to cornering loads than other carbs because theyir design has air intakes (for the emulsifier tubes) at the top of the bowl - where I think they are prone to having fuel splash in. I have DCOE's on my PV, and they might not act quite the same as a DGV, but from what I've seen most Webers have a similar design, just different overall organization. My DCOE's will go lean if cornered hard in one direction, and go rich if cornered hard the other way. I'd just notice a bit of a bog if it wasn't for my wideband O2 sensor telling me what exactly was going on.
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I'm JohnMc, and I approved this message.