Overboosted steering

I've got a situation and I need the collective brain power and past experiences to solve it. My '78 400 power steering box was rebuilt to stop a slow leak, however, the guy who rebuilt it found, maybe, an extra part. It was a large ball bearing that happened to fit in the threaded tube that accepted the supply line banjo bolt. 'Maybe it's a check valve' he said. Uh, ok, you're the expert. I install the box, install the left front suspension and eventually fire up the car. Nearly instantly the box starts spewing ps fluid. We determine that it certainly was a check valve and not where we wanted to have one! The blockage blew out the seals...
Ok, strip suspension and remove box to replace seals then reinstall. It seems the ball bearing WAS an extra part that found its way onto his workbench in the months while he was 'waiting for parts'. Fire it up again and no leaks from the box but I find that the steering effort is ridiculously light. My gramma's '73 Cadillac had heavier steering. The wheel practically spins itself.
There is a slight leak in the hose from the reservoir back to the pump but a dye test suggests it's in the banjo fitting so that will be replaced. I don't see how that would relate to the light steering effort anyway.
What's happened?
How do we go back to normal steering effort?
One theory is that the box is actually fine (now) and that there is a pressure relief valve in the pump that is jammed open due to debris or some reaction to the ball bearing incident and that the system is overboosted. While the car is drivable the concern is that the high system pressure will eventually blow out the seals again. I've never seen a schematic of the box or pump so it's hard to know where to start.
Has anyone here opened up the ps pump and can verify there's a control valve of some sort in there? The pump and box on this car is the same type found on the 365gtc/4 so I'll post on the vintage forum too.
Thanks for your opinions.

 

Yes Bill, the fluid lines were replaced! I didn't see the restrictor at all. Maybe it's a standard part from a hydraulic shop?

 

Really, it's comically light. Now if I had an automatic I could recline the seat, hang one arm on the sill, drive with my knee and keep a beer in the right hand.

 

It turns out that this is a fairly common issue in the hot rod world and also with off-readers with custom steering boxes etc. As Bill notes, there is a flow restrictor in the hose. The same principle can be found in plenty of GM and ford cars so there's no Ferrari magic here. A PO replaced the supply hose without a restrictor and my guess is that after I had the steering box rebuilt, fluid change, new ball joints, etc to reduce friction and drag the steering is now really light. The danger in having too much flow is that in some situations the pump might not be able to keep up and it will cavitate and squeal. I haven't driven the car hard so I haven't seen any issue other than the crazy light feel.
A new ferrari hose is $300 but my local hydraulic shop will make up a hose with restrictor for $50 so I'm tempted to try that first to see how i control the effort.
The hot rod guys often match Mustang steering racks and GM engines so there's actually a market for adjustable flow valves. Mitch, I know you've got a lot going on these days but you might consider fitting a valve like this if you want to lighten up the steering in your car.
Turn One
It's a reversible mod so don't worry about the Polizia from Maranello.

 

In the interest of time I installed an oem house from eurospares. The oem house with flow restrictor does not increase steering effort over a plain hose so my steering is still too light.

 

I dug into the ps pump tonight. The pressure relief valve was easily removed and disassembled.
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There's a small hole that may have been plugged or the small ball that works as a check valve may have been jammed in some way.
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I can bolt it all back together, fill the system with fluid and find that effort is back to normal.
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May be possible by adding or subtracting shims on the end of the valve body. Mitch,you should compare this to the check valve in your 365. My car has 4 thin shims. I'll measure the total thickness before reassembly.
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Installed the valve, new crush washers and filled and bled the ps system. Effort is still far too light. To recap;
New hoses & fluid
Disassembled & cleaned check valve
Rebuilt steering box
New ball joints
correct tire pressure and front end alignment

Steering effort is 1-finger light at all engine speeds. Vey frustrating.