I'm in the same dilemma as the OP - picked up a used 12ohm two10 and ordered the 4ohm conversion kit from Alex.
Mine did come with full instructions, and they emailed them to me as well in PDF, so if you'd like them, let me know and I'll pass it on.
Haven't done the conversion either, I've gigged and rehearsed it at 12ohms, and that was only with a TC BH250 head, and had no problems at all.
Having spent on the kit, I kind of feel I should get it done, but it really works fine as it is.......