It's no secret to 49ers fans what their team's two biggest needs are in the three-day NFL draft that begins Thursday.San Francisco needs a fast, field-stretching wide receiver and a cornerback who can make a solid contribution to the defense in his first season.There are other needs, of course. The team needs depth at outside and inside linebacker, safety, center, tight end and perhaps at quarterback (for the future).But with 11 picks in their pocket, the 49ers already have a strong roster, and certain positions (along the offensive and defensive lines, for instance) already are very deep. So it would make sense for the 49ers to go all in at wide receiver and cornerback. The 49ers should not only use their No. 1 pick addressing either of those positions, but use four of their top six choices on wide receivers and cornerbacks.San Francisco has a No. 1 (30th overall), two No. 2s (56th and 61st) and three No. 3s (77th, 94th and 100th). In order to ensure that they get the best chance of finding what they need at wide receiver and corner, the Niners should target at least two wideouts and two corners high. Mock drafts have the 49ers taking an assortment of wide receivers (Kelvin...