Tom M has determined that BLI hoppers will not accept Kadee coupler springs:
If it has not been already noted, the Broadway H2A coupler pockets will not accept the Kadee #5/58 coupler spring. The pocket’s design is not long enough. There are two pocket cover alignment tabs in the way. Also, even if you could get the spring in (by milling the tabs out), it lacks adequate depth. As a result, the coupler will not pivot when the cover is screwed down.