Differences between 3100 beds 47-53 and 54-early 55

[DENALI]

I am working on a 54 3100 and would like to use the art morrison frame assemby. They say their frame is for 47-53 only because the beds are different. They claim the cab of the 54 will still mount just fine but that i would have to change beds to a 53 or older style but they cant tell me why other than their "engineers" said it wont work. I am hoping for some insight into this from you guys and i also hope its something that i can overcome on my end with modifications to make my 54 bed work. Thanks

ETA, maybe what i should be asking is what would it take to make a 54 bed mount on a 53 and prior frame and make it line up correctly?