Calculations

Games Behind

GB = .5*(Wins (1st place) - Wins (team) - Losses (1st place) + Losses (team))

Percentage

Percentage = Wins / (Wins + Loses)

Power Rating

Win over A-league team 3.2 pt
Win over B-league team 2.4 pt
Win over C-league team 1.6 pt
Win over D-league team 0.8 pt

Loss to A-league team -0.8 pt
Loss to B-league team -1.6 pt
Loss to C-league team -2.4 pt
Loss to D-league team -3.2 pt

Power rating for a tie is the average of a win and a loss

Tie vs A team = 1.2 pt
Tie vs B team = 0.4 pt
Tie vs C team = -0.4 pt
Tie vs C team = -1.2 pt

Every game has a 4 point swing on your rating.

In this scheme, a .500 team in A would rightfully be rated higher than a .500 team in B and so on. The best teams in B would probably move ahead of the worst teams in A and so on. You could have 0 be the average team (below average teams would have a negative rating), or you could make 50 or 100 be the centerline. A C team that lost every game on their schedule would have -56 points, so it is unlikely that anyone would go negative if you made the baseline 50. Another thing that would be cool is that if a forfeit counted less (maybe 1/2) on your rating - I think forfeits are entered as 7-0 scores. You could also count run-differential (divided by 10 or so) towards the rating, but this might encourage running up the score.