It's been done on some 99-04 cars, as said most were GT's.
I'd subscribe to the v6 to 4v swap by bluegt96. Similar, but imo a more feasible swap that is actually happening on the forum, not just a theoretical.
V6 to Mach 1 Swap
12 Black GT500 SVT PP l VMP TVS l JLT123 l O/R X l 28x11.50Rx15 M/T Street R's l BMR Suspension l Recaros
03 Sonic Blue 3.8 / 17 Magnetic Fusion Sport 2.7 EB