As Paul sez it would be nice to have a Y8 parts car.
Just a few things to consider... You'll need throttle linkage, exhaust, radiator, possibly convert over to 12v ('56 starter and generator are 12v), Y8 clutch parts, etc.
As mentioned above... there is the 6v / 12v question, that's a whole 'nuther thing.
If your '54 is still 6v you can leave it that way. If you want 12v just for better tunes it can be done without changing the whole rest of the car.
If you find a 'good' used y-block engine double check to make sure the rocker arms are/were oiling properly. Small and clogged oil passages to the top of the heads are one of the weak spots of these engines.
'55, '56 and '57+ y-block engines are not always the same between the years and have some parts that aren't interchangeable. Whatever you find, get as many of the original parts that were with the engine as you can. The carb, dist and intake manif setup is one of the things that can sneak up and get you.
This info below was written about the 4bbl engines but may(?) be similar for the 2bbl engines, I hope someone else can provide more/better info.
In '55 the choke heat hardware for the teapot carb was mounted in the manifold (ECB-B) not on the carb. and the carb has a single vacuum port for the distributor.
'56 teapot carbs on a '56 ECZ-A manifold have the choke thermostat on the carb and dual vacuum ports for the dist that also had a dual diaphragm vacuum advance unit to match.
For '57+ Ford changed again and didn't use the teapot style carb, and the top of the intake manifold (ECZ-B) has a different bolt pattern for the new style carb. They also use a different/better style distributor.
Don't let someone give you a 'good deal' on a 239, they're super hard to find some internal parts for and not even worth the trouble of hauling it off.
You might not see it at a glance but the radiator is different for a V8. The core is the same but the mounting brackets on the side of the radiator are different and the tanks have larger radiator hose inlets on the V8.
If your old 223 I-block 6 is salvageable, there might be people on www.fordsix.com interested in buying it. Lots of people who post in the vintage inline sixes section of the site are owners of the Ford 215 and 223 engines.