Can I run a s4 switcher & a alcoaF2a as a double header
I think those are both DCC-equipped. You can either set them to the same address or as a consist and they will run together.
They are both DCC, Will it hurt them to run as a double header. But they run at different speeds.
This is where speed matching comes in. I don't think the Bachmann decoders in these locos support CV's 5 and 6. You may want to replace them with ones that do. They should be the kind with an 8 pin connecter on one end. Google speed match DCC locos for more info. Sondtraxx and Digitrax both sell motor only decoders with the 8 pin connecter. Joe