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As has been said here many times, dollar for dollar you will be able to get more out of the 400 compared to what the hassle and price of the 460 swap will set you back. Also the 460 weighs more. If you had both engines side by side and there was no difference in installation between the two then the 460 would be a more attractive option, but thats not the case. Besides its nice to tell someone that remarks how well your truck runs, that it's a 400. They don't expect that.
What are you going to be using the motor for??
With Cleveland heads, are they the 2v or 4v?
You will probly get more power out of a 429 for a little less but as Tastyklair said, just having a motor that is often overlooked is always a cool thing to do.