I have found both these motors for sale locally and am trying to figure out which one would be better for my boat. The guy says headers and everything from my old 454 will fit on the 396....any truth to that. Also will my rail kit work with a 396?

Ginger or Maryann    Betty or Veronica 

Caution.... 454 has counter weights for balancing on flywheel and harmonic!

396 does not !! 

Go with the 454

imo you can get more rpm out of 396 but that was in a car!

I have found both these motors for sale locally and am trying to figure out which one would be better for my boat. The guy says headers and everything from my old 454 will fit on the 396....any truth to that. Also will my rail kit work with a 396?

While the two engines should both fit, 58 cubic inches should net additional horsepower and torque given equal matching of components.  If you plan to put them straight into the boat, you need more information to make an educated choice.  A "performance" 396 may outperform a stock truck 454.  Also, if the 454 is a 1991 or newer engine, it will have parts that are different than the earlier ones.

Heres a little "thread jack" twist This is a BBC 434 (396 with a 454 crank) theoretically makes Mad HP and Torque (450ft lbs at 4K) and turns an AA impeller 5100 rpms
This is becoming popular with the "number correct" car crowd and a very nice motor to build as well , requires "serious balancing" but make use of those 396 blocks 


PSS other than the internal and external balance issues (flywheels and dampners)  (OEM), the motors prior to  Gen 5's are nearly indistinguishable , Love them 427's too , bad ass stuff !

Okay, now that makes sense