All the Ford v8's I've had will siphon oil from the valve covers through the pcv system into the intake if the mounting point into the intake is lower then the top of the valve cover. Some are worse then others.
Small amounts of oil are ok as they tend to lube the valve stems beneath the seals but will eventually cause a large build up of oil on the reverse side of the valves which could crumble and get into the cylinder.
I prefer to install an oil sepereator in the line since it is virtually impossible to get the entry point into the intake manifold high enough to stop the siphoning.
The worst I've seen was my parents '76 Granada with a 2v 302. It was completely stock and untouched by me. They took it on a 500 mile trip new and when they came back there was no oil in the engine at all. So personally I learned to always check the dipstick everytime I stop for gas.
My Webers are plumbed for vacuum on all 8 cylinders and I don't see any evidence of the oil siphoning with the separator but the contents of that catch tank is usually a slimy mix of water mixed with oil.
Most people running a 48ida system are venting the valve covers to the atmosphere with vented caps so you don't hear much about this scenario but within recent years it has been documented that the engine will benefit with better ring sealing with a closed pcv system and there are dyno tests around that show about a 25hp gain using it.
To my knowledge that was NEVER a consideration in the '60s when the ida's were originally applied to US V8's for racing purposes.
Part of that black residue accumulation that you see with ida's in the exhaust is oil blow by in the cylinder and anything you can do to get a negative pressure in the crankcase will reduce the cylinder washing caused by the fuel shot from the accelerator jetting.
Cylinder washing, in this case, is the fuel mixture washing the oil off of the cylinder walls that is there to lubricate the piston rings.
To reduce some of the cylinder washing, you can reduce the pump shot jets down from the stock 2.0's to .5's but that makes starting the engine cold difficult. You can compromise at 1.0's without any noticeable difference power or starting wise but some experimentation on your particular application is necessary.
Ride behind a 48ida equipped engine and watch the exhausts when the driver WOT. There will be a cloud of black smoke and that is largely oil.