UPDATE (1 PM CST): As of 1 PM, I'm now projecting a Franken lead of more like 70 votes, which would bring my numbers closely in line with the Star Tribune's estimate.
This is fuzzy, fuzzy math, but with Norm Coleman again converting only a very low percentage of his challenges in counting this morning, I am now projecting a Franken lead of something like 40 votes after all challenged ballots -- including ballot challenges withdrawn by both campaigns, and special circumstances ballots -- have been processed.
Specifically, I have Franken taking a lead of about 430 votes after all challenged ballots are processed this afternoon. This includes "blue folder" ballots flagged (mostly by the Coleman campaign) for special circumstances. The Canvassing Board ruled this morning that they will evaluate blue folder ballots based on the markings on the ballot only, and will not consider the special circumstances behind them, which are outside of its jurisdiction and instead the subject for a court challenge. As such, very few of these types of challenges are likely to be successful, at least in the immediate term. Coleman has significantly more blue folder challenges than Franken, and so this is likely to add to Franken's total.
I then have Franken losing a net of about 385 ballots once withdrawn challenges are processed, as Franken has more withdrawn challenges that Coleman, most of which are Coleman ballots. This would leave him with a small surplus.
These assumptions are calibrated off the Franken campaign's assertion that it was ahead by 4 ballots, assuming that all challenges would be rejected. This implies, for instance, that a slightly higher percentage of withdrawn Coleman challenges will be converted to Franken ballots than the other way around (not all withdrawn challenges will produce a vote for the opponent, since some were made to ballots deemed to be illegal that the campaigns were hoping to get counted for themselves).
If the Franken's campaign assertion is wrong, that will flow through to my assumptions, leading my math to be wrong too.