machyoung, here are some things to consider.
First, you are saying this is an original, untouched, 58,000 mile 428. Neat to find this long after production.
This first fact needs to be addressed in order to keep your 428 running well into the future.
A few things have happened over the years, one of which is age related parts deterioration. Your valve stem umbrella seals are no longer seals as much as hard as glass brittle, umbrella shaped, black things that will end up pulverized and distributed throughout your oiling system.
I would be VERY surprised if there is not fractured umbrella seal in the oil pan, and head oil return ports, already.
At best the valve umbrella seals are still intact, but no longer providing much in the way of oil control. When you run the engine the oil pump overwealms the oil return system and the area under the valve cover floods with excess oil...and this is when everything is working properly.
Add to this mix the broken umbrella seals blocking the oil return passages and the problem compounds.
With the glass hard, or fractured, or simply broken away umbrella seals you have valve stems with little to no valve stem oil control, as well as an oil flooded area causing the rear valve stems to be potentially submerged in oil.
This will result in oil being pulled, by vacuum, past the intake valve stems and into the combustion chambers...and now you have a low flying crop duster effect that is especially fun at idle.
Unless this is a true Concours style event car, with an awesome preservation class engine, I strongly suggest you pull the valvetrain to replace the valve stem seals with something that will actually seal and control oil and air past the valve stems.
When doing this it is a great time to install the restrictors.
Pulling the heads and having them inspected and gone through would be the best option to ensure things are still worthy of running the engine as intended.
If you install an improved oil pump per the general rule of FE engine building lore, usually a high volume pump, then it is really wise to also install the head oil flow restrictors.
The oil system on an FE is a bit unique in that it is best to treat it like a fully cohesive system rather than a collection of parts.
In stock form, on a stock engine, with zero alterations away from stock, it works pretty well.
Start modifying any parameters away from that and the entire oil system should also be modified in order to work best as a whole oil system.
Many a well intentioned FE owner simply installed a high volume oil pump when they had the oil pan off for some reason...and the results were more damaging than if they had left the oil system alone.
There is more going on here than simply dropping in a Holley jet of the proper size to restrict oil flow to the heads.
While you do not need a full tilt, race inspired, rebuild to get you to the good results, a bit of prudent preventative maintenance and modification can be just the thing for decades of fun driving in your situation.
One benefit of doing the head work is you will get to visually inspect much of the engine while doing the work. This can either confirm things are still good, or give notice that other, more involved, work is required...which can be the bacon saver as compared to finding out your engine has issues AFTER it broke on the way to Cars and Coffee.
