Ilford comments extensively on cold cathode printing with their products in this document which is worth reading if you have cold light and want to do MG printing: http://www.darkroom.ru/info/manuals/...manual_eng.pdf

Nothing wrong with making a LED head but I'll bet that cold cathode works fine.

Since you want to do multigrade printing, I'd check this out!
...pile of Chromega 4x5 heads...

http://www.apug.org/forums/1001250-post4.html