I once had an army technical manual on welding (great book that) can't find it now but it did address welding armor plate. Search on Google indicates it may be TM 9-237 but no source to buy it appears. If you could find depot maintainance manuals for American Sherman tanks (one model of which had welded armor) that would probably do. An obvious source of info is the manufacturer of the plates you intend to use.
Good luck
Bill