Werra, glad I could be inspiring! Randy, I remember our emails. I've experimented with white LEDs from 7000K (cool blueish light) to 2900K (yellowish). I had some troubles with the 7000K--which I now think was a flaw in my testing procedure--but regardless I wouldn't suggest 7000K white LEDs because the greater bias of blue color raises the unfiltered values of variable contrast paper. Even with filters 7000K was tricky to print with, so again I wouldn't suggest that color. 5000K to 2900K worked just fine in my experiments and in my working LED head. Printing times with a normally exposed 4x5 neg in my LED head are roughly from 3 to 15 seconds with the lens at f/11. The longer times are with filters used.
Mainecoon (I like that name) I'm sending you a PM.