I'd go 440, Cheaper & more durable, you can get 500 hp from a small block, but it's going to be a Big cam, high compression & high RPM sort of deal, not the greatest for a heavy B-body....... 440 man .

 

you can use a 904 behind a 340/360 but its not recommended because you'll most likely blow it up unless you get a high dollar transmission kit for it. you would want a 727.

however i KNOW you would have much more fun with an A833 4 speed.
since you're swapping the engine out anyway, get a 360 or 340 thats set up for a manual.

why you should'nt get a big block: a big block will add about 150 lbs at least in the engine alone. then you will have to worry about the necessary suspension setup mods - springs a-arms, whatnot that will have to be beefier in order to support the heavier engine. that also adds a significant amount of weight and not to mention all the work needed to get the big block to fit in there. and when you do get it in there, if you want to run power steering AND headers, you will need to buy a very expensive set of headers designed to fit in a B body that has power steering. (the clearances get very tight with a big block) The OTHER reason, is the way your car will handle. all that added weight is gonna make your car understeer, and it wont handle nearly as well as you would with a small block. plus all that added weight - especially in the front - will be much harder on your brakes and you will take a LOT longer to stop unless you put some good money into brake upgrades.

why a 360 is perfect for your car: you said your other choice would be a 340 or 360. well a 340 is a nice high-revving engine, but it makes most of its power in high rpm's and not too much down low. and a B body is a fairly large car. while the 360 might have been considered a "low performance" engine of its day, i highly disagree. the early 360's 1971-1974 had many of the same parts as a 340. they had the same heads (915 and 587 castings) , valve sizes, (1972-73 340's 1.88/160 valves) same exact forged rods, and the natural advantages of a mopar small block: 18 degree cylinder head valve angle, and shaft mounted rockers. and the real cool thing, is that early 360's could take as big of an overbore as a 340 could. (since the 340 has a stock 4.040 bore, and the 360's bore is 4.000) so its possible to bore a 360 out .080, and maybe .100 (if it passes sonic checking)

the only "non-performance" aspect to the 360 is the cast crank. but then again theres plenty of Ch**y 350's running around out there with cast cranks. the nice thing about the 360 is also the larger main bearing journals - 2.81 as opposed to the smaller 273/318/340 2.50in journals. and if you get lucky - '74 and '75 360's had a shot peened cast crank - which would be a little stronger.

and a 360 will make enough low-end torque to keep your car happy and making it easier to roll out the clutch. it shouldnt cost too much to have the intake valves machined for 2.02in if you like, and a mildly built 360 can can handle spinning 6000 rpm. which is pretty good for a motor designed with low end torque in mind. and if they can make a budget 318 with 400 hp, then you can easily have a 360 making 400+ hp

 

lol damnit i just love small blocks.

maybe i wasnt thinking clearly. i do know that you can build a nice 408 stroker outta a 360 with a 4inch stroker crank...

but then again, i really like 383's, since like most big blocks they can actually rev...

fine whatever. get a damn big block. just swap out the auto tranny for a 4spd...

 

It's my 78 Chrysler Cordoba, 400,727, I had N20 on it for a while, it ran low 13s @ 104 mph. This summer it's getting a 10.5 to 1 440 with Edelbrock heads & dual quads !