Hi.These are by Rivarossi.
I have the "Timberjack" set with 4 cars plus Heisler loco and have replaced the couplers with McHenry No. 56.
The couplers just pull out and the replacements pushed in and work very well.
Kadees can be fitted but requires modification to the coupler housing which is NOT to NEM standards.
Hope this helps. Colin.