When an M7 rescue has to be made with the Harold protects (or any engine) a compromise coupler is used.
Which brings up another important difference between LIRR M-7 and MNR M-7a.
Since new MNR M-7a cars are transported on their own wheels, these cars have a "DB-40" unit added to the braking system, which enables a locomotive brake pipe reduction brake application in those cars, when cut over to that system. LIRR M-7 cars do not have a DB-40 unit, since they are transported on railcars. Perhaps this would have been something to put on our cars, anyway, methinks.
Without a DB-40, or an M-7 coupler setup on the protects, a rescue engine can only have brake application in the crippled M-7 consist by dumping brake pipe. (Service brakes must be cut out in the entire M-7 consist.) It's either all or nothing (in the towed consist).
I don't know how much a DB-40 costs, but I think we should have added them, even though they hopefully would not be used on the LIRR very often.
The LIRR maybe got scared off because of the experience with the M-3 "Triple Valve", which was supposed to provide a similar function, but was so problematic, thay were piped around and removed from the entire M-3 fleet a long time ago.
Tom