Hi Frank,
I can provide you with a project-open 5.0.3 container running of openacs 5.10
It has errors, so you will need to manually go through each of the packages and figure out (systematically) where PO Is still using code that should not be there. (And I did not do it. Just remembered that task from upgrading to OpenACS 4.8)
When I looked at that container some months ago, I think the biggest challenge was the database upgrade from 9.2. to 10.x and higher. That was, if I remember correctly, due to a change in tsearch. Which OpenACS takes care of but PO has its own thing for full text search so I think something there did not work out.
I‘d love to help, but given other engagements (encouraging older developers to adhere to coding standards which have been around since XP, not to mention automated code generation) as well as our transition to OpenAPI based coding (lets say we learned a lot and the amount of technical debt shows it 😊), I can*t
Let me know though if I should build you a pipeline for oacs-5-10 based container. This checks out oaks-5-10 based of Naviserver and loads PO packages into it in a second stage. I think it is already on dockerhub at hub.docker.com/sussdorff/projop:oacs-5-10, but I might be wrong.
I would highly recommend by the way to NOT fork the OpenACS packages, but just use the standard ones and only if there is a very good reason and unwillingness of the community to take the patch and no other way to make the functionality work, to for that single package. I know, painful, but you get used to it (at least I got with PO 5.0 after going the fork way with PO 4.0).