dread - yes, and that forum is very accurate with information. mags are the same, barrel's are the same, except for the MTR barrel with the tighter chamber but if you really wanted to put that on a 455, there is backwards compatibility. the current unknown is trigger compatibility. i emailed with Timney last week and they are not sure if their 455 trigger will work as they haven't gotten a 457 in the shop yet.
there is one known INCOMPATIBILITY and that stocks. the 457 is a different footprint so it will be all new aftermarket chassis and stocks for it. i do know MPA is working one, Manners will have one and I've heard some others will as well.