We did build a couple of V-12 modular engines at Ford, by sectioning and welding 4.6L blocks and heads. All that was needed was custom cranks and cams.
One ended up in the GT90 show car, and the other one got stuffed into a Town Car! Engine management was done by a pair of modfied Thunderbird EEC-IV ECU's, so essentially the V-12 was tuned as a pair of V-6 engines.
Upper management killed that project off pretty quickly, once they found out what the "Welding Feasibility Study" really was LOL!