i wouldn't touch it personally. % of players tied or winning going into the last round of a tournament is historically around 20-25% I believe (at least over the past 4 years?).
I think anyone within 4 shots of the lead right now has a chance. Given how hard the first 6 holes are playing a lead can be erased quickly.
McDowell folded earlier this year when he was H2H with Tiger if I remember correctly.
Field is -335 against Furyk, why not throw a few on that line to cover your original bet and then a little on top, then sit back and enjoy pulling for your guy on Sunday?