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I also learned the hard way never use plastic fuel filters, always get the metal can. I drove my truck to the garage for its yearly emission test with gas spurting under the hood as I drove into the shop. I was so lucky it didn't start an engine fire. I replaced it with a metal one in the parking lot and will never use a plastic one again.
My experience with Edelbrock carbs is a bit different. I’m not a carb genius nor have brand loyalty but have 2 Eddy carbs on squares coincidentally. 1 is idk probably 15 years old at least. Other is only a few years old. Both trucks start very quick sometimes instantly when cold but driven recently. Both also start reasonably quick after sitting extended periods. The old one just sat for months, started it last week. Only cranked a couple seconds before starting. It does have an electric fuel pump that primes for 3 sec key on though. Newer carb is mech pump.
The pump has check valves to prevent fuel drain back. But that's irrelevant the needle and seat is in the top of you carb so it can't siphon the bowls dry anyway,the idle air bleeds may be plugged and the idle circuit is siphoning the bowls dry through the idle circuit. So all that fuel is running into the manifold and cylinders when Parked. Which would cause or contribute to your oil been contaminated with fuel. I was in a big hurry earlier,didn't read your entire post. Sounds like your fuel pump ruptured and us filling the crankcase with gas,once overfull and thin on viscosity oil can be coming fron to s of places. Do you have factory valve covers,a pcv valve and either a vent tube or a breather in the opposite side valve cover?
It's a check valve in the fuel line issue. The edelbrock carbureator needle and seat is on the top of the carb fuel spill in from above to fill the bowls. Even if it did start to syphon,which could be possible to syphon through the return line on a 3 line pump. It shouldn't be possible to syphon with a 2 port pump unless the pump itself were starting to fail. The pump has 2 check valves in it. Now even if a syphon started it would stop as soon as the bowl level dropped Lower the the seat because then the needle and seat would be above fuel level. Like trying to syphon gas with your hose above the fuel level. The idle orifice is the lowest port and it draws fuel from the bottom of the bowl. There is an idle air bleed that should prevent the siphoning. But if the idle air bleed has dirt in it the idle circuit can syphon until the bowl is dry,because it draws fuel from the bottom of the bowl,and the outlet is lower than the bowl.
