Not a definitive comment, for sure, but my Lionel Clinchfield coal-burner (what else?) Challenger from, I guess, 2010, has no apparent lifter mounting holes. That may be true only as a model manufacturing/specific road decision, though, as the CRR locos never had lifters..
(The Clinchfield did indeed have several "late UP-design" Challengers after WWII, bought from the Rio Grande. The UP itself never actually owned any of this particular group of "UP" engines.)