1/4" is probably enough. It won't be much wider than the stock perch and part of that little "overhang" will be filled with weld, so the edges shouldn't bend. 3/8" wouldn't hurt though if you want to err on the side of overkill. <img src="/forums/images/graemlins/smile.gif" alt="" />

'97 4Runner, '06 F350, '86 4Runner, '05 WR450
http://home.4x4wire.com/erik