"Paul Corfield" wrote

Gospel Oak can take 4 cars [1] but not longer because trains would
foul the points for the through tracks used by freight. To extend the
bay would require a new bridge capable of tacking 3 tracks. That
assumes you can build it and / or obtain permission to do so.

The Sectional Appendix suggests that all platforms on the Goblin line can
take a 4-car train, except South Tottenham (up platform at 81 metres nearly
long enough, but down platform at 52 metres a long way short), and
Blackhorse Road (both platforms 84 metres, so nearly long enough). The
Gospel Oak bay can take 4 but not 5 (97 metres).

Peter