I'd heard that, but if you look at the construction tender, the original closing date of December 6 has slipped to January 31. This makes me wonder if construction won't be starting in February, and bustitution will be delayed. Though it wouldn't be the first time that TTC switched to buses long before construction started.... yes, construction bustitution does start on February 17th for 501L
Though the bigger impact is not the 501L bustitution but the ones for 501A and 504A, which reduces the streetcar demand by another 14 or so cars.
They will also freed up 8 cars from 503 with the January 6 2019 board, and the was 8 cars from October 2018 when they cut back on the 504/514 service. That's at least 21 and up to 37 cars available for additional service, somewhere.
It only takes about 12 CLRVs to run 511.... but those 7 could also be used for 511.
Additional options are the 4 or so cars needed to remove AM peak buses on 506, 7 cars for 502, and 18 cars for 505.