Are the MTH Railking F3 and Williams F3 the same body shell?

@M. Tyler, I do not believe they are they same.  Comparing my MTH RK Chessie F3 to my Williams Great Northern F7, the tip of the Williams nose is flatter, not as much as an ALCO FA or PA, but just a bit.  Not sure when True Blast II replaced True Blast.

I'll try to get some pictures tomorrow.

Coach, if you are comparing your F7 it would have it's origins in old Kusan tooling which is quite different than the Lionel/Williams F3's.  The RK is a very close copy of the Lionel classics. Perhaps you could post a photo of yours as if I recall, the windows are considerably larger than the classic  'squint' of the Postwar F3s

Could be Jerry shared with or sold the molds to Mike, so they might be the same.

Compare the MTH and Williams F3 with the postwar Lionel F3 shell. The Williams and MTH versions are meant to be copies of the Lionel F3, which also makes them copies of each other by default.

SO here we have a MTH RK Chessie F3 and a WBB Great Northern F7.  I was not aware that Williams and subsequently WBB had two different molds for the F3 and the F7 when I chimed in earlier so this doesn't really address the OP but from the photos these two are definitely not from the same mold.  WBB is longer and wider, has a more blunt nose, fan housings are shorter, some extra vents and/or exhaust in the roof, possibly for a steam generator, two horns and larger front windows as C Sam pointed out.

I think ^^Sam Jumper explained it best.  Coach Joe, the reason for the confusion is that there are at least two styles of RailKing F3's: the stubby one you have in Chessie paint, and the longer one that is meant to be a copy of postwar Lionel.

Likewise there are at least two Williams F3s: the first, flat-nosed one derived from old Kusan tooling, and the second one that was meant to be a repro of Lionel postwar.

To determine if both shells really came from the same mold, you might look inside to see if there are bumps or dimples where they were cut from a sprue, or pushed out of the mold.  Interesting thread!