Valve timing on many engines w/overhead cams can be tested by temporarily taking the timing covers off. All you need is to be able to see the timing mark on the camshaft sprocket and the crankshaft pulley at the same time. I’d do that first before removing the engine. Pinging is most often caused by an ignition timing problem or spark plug gaps too wide. Both are easily tested. The more you describe the symptoms though, to me it sounds like an exhaust leak. It could be sourced anywhere from the exhaust manifold and the muffler. And it wouldn’t be at all unusual for it to happen only after the engine is warmed up, due to thermal expansion of the crack.
If you want to remove the engine and fix everything up at once, no harm w/that. Sometimes that is the fastest and easiest way to get all the deferred maintenance done at once.
Oil leakage on older engines is often just seepage past old, worn gaskets that have been so compressed for so long that they’ve lost their resilience. There’s no pressure anymore to keep the oil in. Along with that, oil seepage past the rubber seals at the ends of the crankshaft (and, on in-block camshaft setups the camshaft). The crankcase often becomes pressurized due to blowby and/or plugged PCV valves, and that can contribute to the seepage past he rubber seals by pressurizing the backsides. On distributor based electrical systems, the rubber ring around the distributor shaft can leak too, although that’s not one of the “biggies”. Seepage around the oil pan gasket is common on old cars too, again due to the pressurization o f the crankshaft.
Most of this oil leakage has no effect on the engine’s life or operation as long as the level is kept below “low”. It can burn if it runs onto a hot exhaust, and can be messy, but it doesn’t affect engine operation.
Fix the operating problems, the pinging and the knocking. Any gaskets you have to remove should, as always, be replaced with new ones, but don’t focus on the oil leaks until the operating problems are fixed. That’s my recommendation.