small block v. big block

I bought a 72 charger about a month ago and the 318 (non original) that was in the car was locked up and i know where a 383 that is running is and am thinking about putting it in the car. I know i would have to change the motor mounts but would i have to get a new drivetrain since the 904 that is with the 318 will be replaced with a 727 when i get the 383?

Actually, I believe you change the "K" member to put the B and RB engines in there. A more knowledgeable MOPAR guy could answer that.
The 383 is certainly a good one, especially a '68-'70 "Magnum" (painted orange, not blue). Big bore, short stroke. Good medium-sized performance engine. With today's technology, though, a 360 might be the hot ticket. A well done 360 will make 500 horsepower and more low-end than a 340. For a drag motor, the 340 is the small block of choice.
There is also the school of thought "Never send a boy to do a man's job", calling for a 440 or bigger, to compete in today's street freak crowd.

Yeah you'll need the other K-member. You'll need a different driveshaft since the tailshafts on the two transmissions are different lengths. So, get the 383 and a 727 to go with it, and the right driveshaft and you're set. Leave the differential alone, I would anyways.

The existing k frame will be fine. In 73-74 the k frame style was changed and there is a big vs Small block version. You simply need BB mootor mounts. The driveshaft as stated above needs changing and the radiator has the outlet on the other side.

The rear is likely a 8 3/4 which will be just fine.

He might need a different K-member yet. It depends what kind of oilpan it has on it. If you take a 361 out of a Dodge grain truck or something you'll never make it fit in there without that other K-member. That's how it is.

Not for the engine choice listed. Besides it would be easier to change the oil pan than change a K frame.

Rkcuda you win! I'll Clear this up cuz i know everyone is posting something about this topic. In 73 and 74 they changed the mounts and k frames. If you have a 71 or 72 charger anything will fit in their, you just gotta make sure you have the right motor mounts.

Well I think i'm fixin to get a 360 so i know that will fit reguardless. The 360's outta a 74 charger and has been rebuilt. Pushin out about 450 h.p. is what the guy told me it dynoed at. Also the 727 i'm buying has been rebuilt.

Get as much of the dyno and build information as you can. You need to know exactly what the fuel requirements are. At 450 horse, it could be a "low" OR "high" compression engine, depending on the direction the builder took.
Anything over 9.5:1 with iron heads is asking for trouble without mixing race fuel into 93. For 93 octane, 9.5:1 is considered the practical limit. There are those that follow the "bigger cam" philosophy to ward off detonation (it will "bleed" off cylinder pressure at lower engine speeds). It works to a point, but not at higher RPM.
Octane boosters are a waste of time and money. Make sure the octane meets the engine's requirements. You can use a 50/50 mix up to about 11:1 (110 racing gas, 93 octane "premium").
That car should run pretty strong with that engine in it. Have fun!

Jim