Yes, that's true.
The 12 Gauge Wingmaster has been the same since 1950, except that 3" and the 3.5" chambers have become available since then. A brand-new barrel will fit a first-year Wingmaster.
However, the 20 Gauge Wingmaster didn't have a scaled frame until the late 1970s. Earlier onese were 12 Gauge receivers, made to fit 20 Gauge parts. Barrels for those tend to be hard to find, and they have not been made for a long time, so they're only available used -- if someone is willing to sell just the barrel, which doesn't happen very often.