Your Crown Vic looks GreaT, Rowen. Diana having been around for awhile, you best determine what you've got before setting out to do too much of changing anything. At an earlier time, if engines needed overhauling or other problems arose, it was common to swap parts at the local junk yard. The economics of installing a good used engine from a car that had been in a wreck rather than having your original engine rebuilt spoke volumes. Too, there was the time factor. Rebuilding an engine can take time, swapping engines or cylinder heads if a valve job was needed saved down time. With the y-block Fords, many components can be interchanged between '55 and '64. Notice that I didn't include the '54s in that statement. '54 being the first year of production for the Y engine, some components do not interchange depending upon whether they were early or later year production.
Besides parts getting exchanged for repair purposes, there have always been the Charlie Brown types in this world who were setting out to 'improve' their ride. Sooo... engine-wise... stock, later year or different model FoMoCo cylinder heads with bigger intake valves or offering a higher compression ratio, better flowing exhaust manifolds, engine blocks with bigger pistons or longer strokes, intake manifolds with four barrel instead of two barrel carbs... the list goes on. ALL of this 'stuff' was easily exchanged and as the cars got 'older' the availability of donor vehicles in the 'junk yards' increased and the cost to purchase the used, improved performance, O.E.M. FoMoCo parts decreased.
The bottom line is that with an attractive, sought after model like your Crown Vic, it will be a bit unusual if you don't have some parts that have been easily swapped for either 'improvement' Or repair purposes of one type or another over the last 60 years of others having owned it.
One of the most common swaps from a practical standpoint on the '55 or '56 FoMoCo y-blocks is the ignition distributor. However, IF you swap distributors to one from a '57 through '64 y-block you have to either change carburetors to a later year one that provides the appropriate vacuum signal for your later distributor OR make a modification to your original '55 (or '56) two barrel (or '55 or '56 four barrel IF you were to move in that direction). Don't misunderstand, there's nothing wrong with your '55 two barrel carburetor. The point is that the '55 and '56 Loadomatic distributors on all Ford and Mercury vehicles had two barrel or four barrel carburetors designed to provide different vacuum signals to the distributor that come from more than one location within the carburetor as the engine operated at idle, under load, at higher speed, and while at cruising speed. In contrast, in the later carburetors (post '56) the vacuum signal comes from a single location within the carburetor to modify the spark advance intended to improve gas mileage when the engine is operating at a constant cruising speed.
IF your ignition distributor has NOT already been changed to a later style unit by a previous owner, and if you do change distributors, you need to make the modification described on the web address below to make the two devices work together appropriately. NOTE: If someone has already changed your engine to a later distributor and did not make the modification to the original '55 or '56 two barrel carburetor, they have created a performance (proper ignition advance) problem, too.
In response to your question about starting difficulty (excessive cranking being required)... I'd check the tune-up of the engine before doing anything like changing distributors. Spark plug gaps, ignition point dwell angle, vacuum line connections between the carb and the distributor, and ignition timing are the most likely problem. Your two barrel carb is down the list of possible issues compared with if your '55 had an original '55 or '56 Holley 4000 4 barrel. A defective vacuum diaphragm on the ignition distributor or the advance plate inside the distributor not moving freely or the distributor cap contacts and rotor having surface oxidation are other things to look at if the basic initial tune-up check doesn't yield results.
IF you do move to a later '57 - '64 ignition distributor (these have the spark advance curve controlled by a centrifugal advance mechanism and a vacuum advance diaphragm) see this web address for the modification to your '55 or '56 two barrel Holley or Ford made carburetor . . .
http://www.eatonbalancing.com/blog/2010/02/07/modifying-the-holley-94-two-barrel-for-late-model-distributors/Hope this helps, Rowen.
Hey! This stuff is supposed to be in the 'Technical' section. You've graduated from 'This-N-That'!
NoShortcuts
a.k.a. Charlie Brown
near Syracuse, New York