How do I get my new BIRT 4.3.1 to use the use the same project and workspace for everything I built in 4.2.1? - upgrade

Question

All of the following is done in a cloned development (VM) server, so there is no risk to my production environments (prd04 for completed reports, tst04 for creation and problem solving, working on clone of tst04 now).
I have been using BIRT 4.2.1 for a about a year, I have several reports and most importantly a library that were created with 4.2.1. While the production reports actually run via Apache, I have downloaded and updated the "runtime" files so any new reports will run ok, but this made 95% of the old reports stop working. It does not make sense to try and “fix” them with 4.2.1 if I am going to be running 4.3.1 now. I expect the problem to be fixed with a library correction related to jar or war file.
I want to use my fresh download of 4.3.1 in the same workspace and with the same project as I used for 4.2.1. But I am days into trying to make it work and no luck.
Failures
Tried to upgrade the existing 4.2.1 to 4.3.1 but never got it to work correctly
Ended up downloading a fresh copy, so now I have two instances of BIRT (one of each)
Used the existing 4.2.1 workspace for 4.3.1 C:\Program Files\Apache Software Foundation\Tomcat 7.0\webapps\Birt
Brought in the Navigator View, but am unable to make it “see” the existing reports and projects
Project > Open Project will not work, “Open Project” is greyed out. If I create a new project “open project” and “close project” works but still can’t “see” my existing project
Open an existing report and try to “save as” in the workspace, but it can’t see …Tomcat 7.0\webapps\Birt
Try to drag (project, library, report) and drop from Resources to Navigator Does not work
Try to drag (project, library, report) and drop from the Window file to Navigator Does not work
Looked into “CVS Repositories” but at first glance it does not seem to be the correct path.
Tried a bunch of other things, but they did not work and were not as promising as the above.
It is starting to feel like I only have two options left;
Create a separate Apache instance for running any new 4.3.1 reports, leaving all the existing reports running on Apache with the 4.2.1 “runtime" files
Create a new project for 4.3.1 and one by one rebuild existing reports, once I have everything working upgrade my production Apache and redeploy all the updated reports.
Screen shot of invisible workspace

Answer 1

Your wrote: I have downloaded and updated the "runtime" files so any new reports will run ok, but this made 95% of the old reports stop working.
What exactly do you mean? Error messages? Hangs? Crashes? OutOfMemoryError?
If it's OOM you probably hit a "feature" introduced in 4.2.2 regarding Default Row Fetch Size (see https://bugs.eclipse.org/bugs/show_bug.cgi?id=407299).
Apart from that, I don't see a reason why any report created with 4.2.1 should not run with 4.3.
And just to clarify: Are you using an Eclipse IDE as a kind of "BIRT Reports Server" somehow? To be honest, that sounds crazy.
We are also using a custom plugin. This was developed with BIRT 3.7.1 and runs on 3.7.1, 4.2.1 and 4.3 without any problems.
The same is true for the BIRT runtime Environment (bunch of JARs, no OSGI). We are not using Apache Tomcat (instead we developed a "BIRT Reports Server").
It should be possible to update the Tomcat Server by just replacing the 4.2.1 JARs with 4.3 JARs and setting the classpath accordingly.