The junction is at 142 St. The southern end of the station (rough guesstimate here) is around 143 St. The station itself is approximately 310 ft long (only fits 6 cars, 51x6=306, round it up to 310 for all intents and purposes.
Once you leave the station, there's a crossover right in your face, a slight curve to the right, and a wide left swing into the station/yard which puts you at about 150 St. Not much room to play with for a diversion for a new tunnel, but it can be done. Just not all that practical.
1. Via Linden Shops. Connects to the LIRR Bay Ridge Branch
2. Via 39 St. Street level connection west of 39 St
3. Via train. Southbound track connected to the LIRR Bay Ridge Branch just north of New Lots Av. Connection removed during the CBTC conversion.
None of them are 3rd rail powered