We know from the MTH website that the "3 rail"[ = TP flange ] Pacific will traverse 042 curves -- so fortunately that leaves just the cars to deal with.
In my opinion and experience -- and I have or had both the 2 and 3 rail versions of these -- it should be readily possible to slightly modify the cars, especially if automatic couplers are not necessary, to be able to take sharper radii curves.
Such modifications could include
- adding washers between the truck and mounting disc.
- removing the springs from the buffers
- replacement of the existing knuckle couplers with drawbars, perhaps between the mounting points for the Kadees.
- mounting the énd steps of the cars to the coupler
and so forth.
Now I admit that I first started modifying Lionel equipment back in the mid 1950's, and you may not wish to change anything from its "out of the box state", but I wouldn't let a little detail like what the maufacturer states to deter me from running these cars on sharper curves -- and, again in my opinion and assuming you really "needed" to run these cars, neither should you.
With best regards, SZ