Monoshock DT250/400 have very, very similar forks to the DT250/360A items, although the upper tubes are about 30mm longer. I'm pretty sure that the bike you got from me has
one of those legs on it.
YZ125C have the same forks, but the YZ items are slightly machined down between the triples (saves weight - about 3gms per leg, I reckon...
_.
The 125C parts are definitely pre-75 legal as they're the same as YZ250/360B. Arguably, the DT-mono bits aren't strictly legal, but they're only a few minutes in the lathe away from being indistinguishable from YZ-B - so I doubt that anyone would care.
DT1/RT1, MX250/360A, and all of the twin shock DT250/360/400s have identical fork legs to the DT250A, but I'd found that good DT-mono fork legs are much easier to get hold of.