leetee...
I believe nearly every one has one leg longer than the other same as we have one foot bigger than the other and one boob bigger than the other. and the body usually learns to cope ...unless it is a greater than average amount which has been properely measured i would not take that as a reason........
no advice for the day than can help...it depends on which tendon and what the damage is to it
better for you to be practical rather than positive...................you have your reasons to do it and so you must focus on these reasons to get you through.these reasons are worth more to you than the chance of a lot of pain and long term injury and expense........
so focus on these important reasons when it gets tough or you have negative thoughts......
I hope that luck is with you and that you manage to run it .or even run/ wlak it without too many problems
good luck