Digital BW, The Print

Yep, Jack. Everything is reversible. What I like is you see the 
changes as you make the adjustments. With Channel Mixer, you try a 
setting, if you don't like it, you undo the change and try again.

I use a blank background layer. I add the red and green files to the 
blue as layers. Then duplicate the background layer and delete 
everything on it. I rename the layers Blue, Red, Green. From bottom 
to top, that's my preferred order.

I turn off the visibility for all of the layers. Then look at them 
individually.

I find somewhere around 5-10% for Blue, 65-80% for Red, and 90-100% 
for Green gives me good initial results. I try various blend modes, 
especially for the Green layer. The final settings will vary from 
image to image, of course.

Cheers,

Mitch