Is there a difference between the two manual flywheels.  I have a 1972 400 flywheel and I would like to use on a 1974 454 motor.  

Sorry man, nothing doing. Your 400 flywheel won't work on the 454. The first problem is the 400 SB is an externally balanced motor, while the 454 is an internally balanced engine, so the 400 flywheel won't work.

Second is the bigger crank flange of the 454 BB over the 400 SB, which makes bolting up a small block flywheel to a big block not possible.  

400's and 454's are externally ballanced the 427'4 396's are internally ballanced but the 400 and the 454 have diffrent ballance weights and or weight placement the flanges on small block and big block chevys have the same bolt pattern and size, all in all you will have to use the 454 flywheel or find some one thart can ballance the 400 might be possible but finding the 454 will probally cost you less now newer 454 are internally ballanced but what you stated you have the older 74 motor. also you can buy new flywheels from parts stores now and are somewhat reasonable priced so check around good luck if you were close to me I happen to have one laying in the garage