Nostalgia & History > How did manual block work on LIRR?

In the 1950s LIRR had manual-block single track
on the east end of the Montauk, the east end of
the Port Jeff, and on the 8.2 miles from B to
Babylon in the Central Branch. No ABS.

The 6/56 timetable says the Montauk and Pt Jeff
were Rule 251-253-254, which I don't get, on
single track, but that's what it says. The Central
Branch says Rule 261-262-263-264. So what's
the difference?

It also says the Central Branch is Rule 316
(no permissive-signal following moves allowed),
unlike the other two. Does that follow from
being Rule 261 instead of 251?

Here are some links that may help.  If you find the answers to your questions please share.
http://www.trainsarefun.com/lirr/signalhistory/signalhistory.htm
https://www.railroad.net/lirr-operating-rules-signals-t9605.html
https://quizlet.com/687264315/lirr-book-of-rules-300-manual-block-quiz-flash-cards/
https://arrts-arrchives.com/bethpagejunction.html
https://www.twinforksnrhs.org/position-light-signals