Marshall 4x12 wiring

I've got a Marshall 1960a 4x12 cabinet, that I want to change 2 of the speakers in. Nothing's wrong with the speakers in it, but they can be a little harsh. The speakers are 16ohm Celestion G12T-75's and I'm going to replace 2 of them with Vintage 30's. My main concern is about the wiring, since Marshall doesn't use your standard jack. The jack has 2 inputs, 1-4ohm, and 1-16ohm, and a switch that makes it stereo with left and right at 8ohm's. I think I understand how this works, but I just want to make sure. For the 16ohm side, the speakers need to be wired in series/parrallel, and the 4ohm side needs to needs to be wired in parrallel, and for stereo, the left and right side each need to be wired in parrallel right? I'll attach a diagram I drew up if it helps any.