Hi Stefan, it IS possible to build a 351W to a 427. Roush and others offer such an engine. Thats a little 'extreme' for me, it's about as big as you can go with a 351W.
Heres a link to a pic of a "Butterfly" Cobra, it appears they may have copied at least some details from the "Butler" style Cobras. Engine placed well back into the passenger compartment area resulting in a rather large transmission tunnel in the cockpit.
Butler was arguably a great design and generally used Chevy power. WISE choice your wanting to go with FORD power!
http://www.crocs.nu/mbrimg/083_pic09...cache=20:46:36