Still I am not convinced that there will be a that much of a gap. Never faced quicks of West Indian quality (Marshall, Holding, Roberts and Ambrose), or a Hadlee (who had the knack of nailing the best opposition batsman cheaply), never played any legendary spinner (don't say that Verity is a legend, and Laker was very inexperianced when bowled to Bradman) in the opposition, let alone on a dustbowl.
But having said that he'll still lead the averages. But not by 40 runs to the next best.
Neither did Sutcliffe, Hammond, Sobers, Tendulkar (save Ambrose and possibly a fading Marshall) or Gilchrist. Yet they're in your all time XI.
Bradman's record is so good it's incomprehensible in any real sense.
We can quote statistics and what-not, but personally I find it nigh on impossible to get my head around a bloke who averages one hundred runs per innings.
The problem with attempting to qualitiatvely reduce his average by X amount given the era he played in is you'd have to do that to the other greats of his era as well. So say Bradman would average 65 today. Do we knock one-third off Hobbs, Sutcliffe, Hammond, Headley, Ponsford, McCabe, Harvey et al as well, such that their averages go from the great to the merely good or very good if they played today? I don't think we can do that to those players.
Great players are great players. They adapt to conditions and eras and styles of play as the game evolves. Bradman did (and would do) the same. Neil Harvey kicked off in 47-48 as a teenager, yet adapted to the game in the 50s and 60s. Hutton played both pre-and-post WW2 and excelled in both eras, despite the changes in the game, the different attacks and the fact that he suffered a serious injury himself and had to modify his game.
Steve Waugh started in the mid-80s, went through all the 90s and played the early part of this century too. He walked away with an average of 50, despite the seat of power in cricket shifting in his time and conditions varying greatly. For his part, Border kicked off in the 70s when ODIs were a novelty and the Windies were just coming to their zenith, and went through to the early 90s. There are many other examples, but the point is great players adapt.
I think it's summed up by what Sampras said of Federer after he beat Roddick at Wimbledon this year - "The great ones, they just have that little bit more". And even among the greats, Bradman had more.