Thank you for your attention!
I opened the card cage and here are the boards installed:
M8190-AB - KDJ11 CPU 15MHz
M8637-EE - MSV11-JE memory....2MB? is this a vax card?
M8637-EH - MSV11-JE memory....2MB? is this a vax card?
M7504 - DEQNA - ethernet adapter
M7941 - paralle interface
M8043 - DLV11-J 4 line serial interface
M7555 - RQDX3 - disk interface
The system has a Seagate ST251-1 hard disk and the RX50 floppy disk drive.
I would want to run TCP/IP...
It looks like the "best" operating system is the RSX-11M+ version 4.6? I'm not sure what the limitations are of uRSX, except for DECnet as previously mentioned.
The memory boards are for the PDP-11. However, I'm not sure if they are PMI or not. But I think they might be. As suggested by gslick, test putting them above the CPU. If that works, then they should work as PMI memories, which have a bit better performance.
You can definitely run any OS on this hardware, which is good. But you are going to need a larger disk... Also, the RQDX controller is pretty slow, so also from a speed point of view, you might want to find some other option. The obvious ideal is to get a SCSI controller, but they might cost you a little bit of money.
As for OS, if you want TCP/IP, your only choices are 2.11BSD or RSX-11M-PLUS. Both will require more disk space.
There aren't that many "restrictions" with uRSX, except that it don't have all the functionality and capabilities of M+. I can't even recall if any of them are significant here, but I have never even tried getting TCP/IP running on uRSX. But V3 is definitely too old anyway. You need V4 no matter what. And M+ is better, so no reason not to switch if you have to upgrade anyway.
Speaking of ethernet controllers, there are some issues/bugs in the DEQNA, but it will not prevent your system from operating. It's just that the operating systems need to poke the controller sometimes because it can hang. But both RSX and 2.11BSD knows this, and deals with it just fine.
The DELQA can give a bit better performance, if that becomes a thing, and it can support network booting. But I doubt that matters here anyway. The only PDP-11 OS that could run diskless, using network booting is RSX-11S anyway.