Other companies have made drop-in PDP-11 replacements
over the years, too.
QEI (based in MA) makes drop-in upgrades for 11/34's, 11/44's, and
11/70's, and Setasi (in Florida) makes drop-in upgrades for 11/70's.
Correction it is QED in MA. I have one of their J11 upgrades for 11/24's - with
docs.
QEI is a DEC dealer.
There is also Nissho that I have seen info on but have never played with.
Yes, I have run RT-11, RSX-11, and 2.11 BSD on systems
that didn't
have a single DEC hardware component in them. (For example, a Mentec
M100 CPU and Andromeda disk controller in a third-party Q-bus backplane.)
The M100 I have in hand still uses the J11 however. I think the latest ones
they went away from real J11's.
Dan