Not, trying to discourage anyone from messing with simh and one of the old UNIX systems - looking at the past. But to be honest at this stage of the game there is nothing in EFL that I know of that modern Fortran can not do. And if you want to see how the world has progressed since F4, and you have a Mac, Linux or Windows box -- the entire Intel compiler suite, including their Fortran 2018 compatible system can be downloaded for free --
Intel OneAPI HPC Toolkit Download This is the compiler many (most) supercomputer codes use - why is a good COFF discussion ;-)
For the youngsters that never saw it, is a piece of F4 code [the Intel compiler can still gork it BTW], which we call the 'Eklund Test' as Dave Eklund was Mr. Fixed format for both DEC and Intel starting in the early 1970s until he retired 5 years ago [note Dave did not write this - came from Europe but is now part of the Intel compiler test suite].
C This FORTRAN program may be compiled and run on a Norsk Data
C computer running SINTRAN and the FTN compiler. It uses only
C FORTRAN reserved words, and contains just one numerical
C constant, in a character string (a format specifier). When
C you run it, it prints a well known mathematical construct...
C
C Even FORTRAN is a block structured programming language:
C
PROGRAM
;PROGRAM;INTEGERIF,INTEGER,GOTO,IMPLICIT;REALREAL,DIMENSION,EXTERNA
AL,FORMAT,END;INTEGERLOGICAL;REALCOMPLEX,DATA,CALL,ASSIGN,CHARACTER
R;DOFORIF=INTEGER,INTEGER;ENDDO;INTEGER=IF+IF;GOTO=INTEGER*INTEGER*
*INTEGER*INTEGER-INTEGER-IF;CALLFUNCTION(IMPLICIT,REAL,DIMENSION,EX
XTERNAL,FORMAT,END,LOGICAL,COMPLEX,DATA,CALL,ASSIGN,CHARACTER);CALL
LSUBROUTINE(IMPLICIT,LOGICAL,GOTO,IF,INTEGER);END;SUBROUTINEFUNCTIO
ON(IMPLICIT,REAL,DIMENSION,EXTERNAL,FORMAT,END,LOGICAL,COMPLEX,DATA
A,CALL,ASSIGN,CHARACTER);RETURN;END;SUBROUTINESUBROUTINE(IMPLICIT,L
LOGICAL,GOTO,IF,INTEGER);INTEGERGOTO,IMPLICIT(GOTO),LOGICAL(GOTO),I
IF,INTEGER,EXTERNAL,RETURN;DOFOREXTERNAL=IF,GOTO;DOFORRETURN=INTEGE
ER,EXTERNAL-IF;IMPLICIT(RETURN)=LOGICAL(RETURN)+LOGICAL(RETURN-IF);
;ENDDO;IMPLICIT(IF)=IF;IMPLICIT(EXTERNAL)=IF;DOFORRETURN=IF,GOTO-EX
XTERNAL;WRITE(IF,'(''$ '')');ENDDO;DOFORRETURN=IF,EXTERNAL;WRITE(I
IF,'(''$''I4)')IMPLICIT(RETURN);ENDDO;WRITE(IF,'( /)');DOFORRETURN=
=IF,GOTO;LOGICAL(RETURN)=IMPLICIT(RETURN);ENDDO;ENDDO;END