Still involved with the Mercury Montclair 292 1955 . The current owner has had a total of 4 Precision pumps installed on this 292 . Only 1 operated at all and that pump would only flow enough fuel to barely keep the engine running at idle .
As per the advice of forum members , I convinced the new owner that the solution to his fuel supply problem was an FE fuel pump . I did install an electric test pump to verify the fuel tank and all lines were clear and supplying clean fuel .
I asked the new owner to call Summit and order an Edelbrock fuel pump for a 1970 390 ford engine , we got that and installed it in minutes and fuel pressure and supply is now correct .
Finally , we took aprts two of the Precision M 34004 pumps to figure out why it seems 90 percent of folks on the net say the pumps do not work . Internally there is a contact point at the pump arm that is put in from the factory just a LITTLE bit off from what it should be . There is no way with the amount of travel available from the eccentric on the camshaft that these pumps could ever do anything . Sorry about that .Easy to tell once we got the Edelbrock  FE pump side by side with the off shore pump , easy to feel and see the difference in the arm operation and easy to see the Edelbrock would do the job the off shore could never do . The ofc shore fuel pump arm moves 1.6 inches and does not even begin to move the diaphragm inside the pump , That pump will pump if you move the arm a full 2.8 inches , ha ha, good luck on that . 
once again thanks for the help to us from the forum answers and members 
Joe in Tampa 

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This appears to be Edelbrock part number 1724, is that correct?
My 312 Mercury has an electric pump which people generally suggest will give up one day. I had one expire last year and was fortunate I guess that it was in the shed at the time.
Is their any reason not to switch back to a mechanical pump like this Edelbrock?

I think that is the correct Edelbrock part number . You should be sure to double check because the owner of the Mercury ordered it and paid for the pump 
If you are asking my personal opinion about the Edelbrock mechanical pump versus the Holley electric fuel pumps , from experience on repairing the oldie but goodies , I would never have an electric fuel pump on board 
only as a possible back up pump for the unlikely event that the Edelbrock failed all of a sudden .
I have owned and driven over 55 different cars , most with mechanical fuel pumps , actually only 5 were newer and came from the factory as such . I have never had a mechanical  fuel pump let me down if it was a good quality brand .
Current local parts stores , including the once great NAPA brand have all gone to the off shore supply that are not reliable . Just read the blogs , the failures are endless .So why take a simple and reliable pump design and 
destroy it because of no quality control and .........PRICE???
It is so bad that if you return any of these failure prone pumps , the know everything salespeople don"t even argue anymore , they just refund your money or give you another defect . Great . A car I have owned since 1981 , 1973  Camaro has an Edelbrock pump that I installed in 1997 and still delivers great performance , but I am not foolish enough to drive all over Florida without a spare ED pump in my tool box .
Again , great forum , great cars , built by real Americans without the benefit of .......................................................................computers !!!