fuel rail swap

Definitely not. That indicates the engine uses an entirely different fuel supply system. You are trying to install the wrong engine and you will likely run into all kinds of complicated issues as the engines use entirely different operating systems. My advice is to find the correct engine.

everything on the 3.0 I want to install is the same as the old one, except the regulator on the fuel rail. Why cant I just exchange the fuel rail from the old one?

Because you are trying to adapt an engine that didn't even come out of a Lebaron that uses a returnless fuel system, among other differences. You already have an issue with temp sensors which control numerous functions in the car. Your operating system needs an exact match.

The old days of "Grab a used engine and slap it in without matching everything to the current vehicle" are long gone. You need to find out exactly what your donor engine came out of. There are a lot of changes in that engines control systems and sensors over the years.

The difference in the fuel rails says you also have different injectors, the cam sensor on your 95 engine is used on other engine years BUT there are two others used as well and only the 1995 version will talk to your ECM. I show 3 different cam profiles and 2 different tone wheels for the cams.

You should be able to use the engine numbers to track it down or ask the place that supplied it.
Then look at its original application.
Looking at Hollander it says you can use the base engine from 1992 through 1995 IF it came out of specific vehicles. Engines after 1995 won't interchange.