I know the Borg Warner T-10 four speed was first made available in the 1957 Corvette, and that it was all aluminum (main case and tail).
It makes sense that the next year's passenger cars might get such an option, but I do recall that in 1959 they were pretty hot items to order from the factory. Wayne Eupers ordered a new El Camino in 1959 and specified the four speed, but it took soooo long he settled for the column shift three speed and bought a four speed over the counter a bit later...
I've never seen a factory 1958 four speed install, but that doesn't mean it wasn't available
. Pretty sure the passenger cars got the iron case version.
TomK