What the after market fuel regulator is suppose to be doing is restricting fuel flow but in the process raises pressure, due to it being before the injectors. Now the built in one on the TBI is after the injectors so that one would have to both of those things.
I found an after market TBI regulator, says it for 5.0 TBI, but I think the 3.8 and the 5.0 regulators have the same bolt patterns. Its call ed a Kirban Adjustable Fuel Pressure Regulator, says it is good for adjustments from 30-100 psi of pressure.
Now for those whos minds think about turboing a 2.8, its possible and may be easier to do with a TBI system put on the 2.8. I know that was kinda off subject but get my gears a turning.