Like you, I wonder about the quality of parts that come from China. Just for discussion purposes.
Inside engine distributors can be heat, freezing cold, hopefully dry air but also high voltage (typically 12 to 25KV). I suspect the outer metal cover of a automotive condenser/capacitor provides some shielding from EMF (the arc across the gap between the rotor button and the wire terminals comes to mind)? For high voltage military power supplies, I've seen removable metal covers over the capacitors.
Almost any .22uF 600V capacitor would work in a clean environment. An external capacitor to the distributor could be exposed to a splash of water from a mud hole, oil leaking off the valve cover, a coolant leak etc. all of which would alter it's capacitance value so it would need to be completely insulated or in a protected box.
If you move the capacitor behind the firewall, to hide it, you need to determine if your length of shielded copper-stranded wire adds/subtracts any capacitance to the original .22uF value.
