I can't understand why it is so hard to find a willing 51, it's a great fighter and can be had much fun with if flown proper. I am still learning it myself, but I allready have alot of fun in it. In the beginning I was afraid to engage the yak3 when it first was presented in AH, it seemed to turn on a dime. Now I think the yak3 is one of the tastier little planes to engage in my 51, they can actually be beaten.
But as a tiffy driver against the willing 51 I'd have to say keep your speed, you will outrun the 51 if you are not too slow to begin with. Or do highspeed turns, ride the tunnel. Seems like the tiffy turns inside the 51 if the speed is in the 280-300 range, but in slower speeds you will have to start making use of that proptorque, the 51 driver will have to chop trottle to make the plane whip over to the right. If you plan your move down low, doing rolling scissors to the right chances are big the 51pilot will chop his trottle one time too much when low and not be able to regain control before he crashes.. That's one way to do it.