Hi, I don't know if this is of any use/interest at all, but I have retrieved an old/early copy of RT-11 Basic (V01-05 18-JUL-73, DEC-11-LBACA-A-LA1) modified to run under V6 Unix, if anyone has any use for such a thing.
I also have a DEC MACRO-11 which runs under V6 Unix, which generates .rel files; there is a 'bind' (written in BCPL) which is a linker which reads .rel files. (There is a BCPL compiler, written in BCPL, to compile it.) Then there are two command 'relld' and 'ldrel' to convert back and forth from .rel to a.out. Noel