I'll admit I haven't seen the NT source but from a user perspective NT's UI (widgets, progman, etc) looked and functioned near identically to Windows 3 so I've always thought those bits were ported over. I'm aware most everything under that was replaced. To my eye that was one step in a well-executed evolution up from legacy Windows towards the eventual convergence in XP.
Probably the only port was Win32s, which was a subset of Win32 backported to Win16.
Win16 stuff runned on a VM like environment, WOW.
https://en.m.wikipedia.org/wiki/Windows_on_Windows