Ache in my foot - pre Youngstown Ultra 50k post!

After the drakewell marathon in August, I continued pushing the miles.  Last week, the bottom of my foot started bothering me a little bit but not enough to stop running.  Basically, the top part (ball of my foot) started aching but I pushed through it.  On tuesday, I ran a light 7.5 miler as my last run before the YUTC (Youngstown Ultra 50k) which is tomorrow.  After the run, I felt fine, went to bed and woke up and my left heel was aching pretty good.  However, the ache that I usually get is on the bottom of my foot under the toes, not the heel...so WTF?  So I didn't run on Wednesday and yesterday, I ran a mile and it didn't bother me.  Today, I am up in New Castle, PA and will be "attempting" the race.  My achilles has been pretty tight of late and I have been stretching it like crazy.  At first I thought, shit, this is PF and it still may be.  I am wondering how it will react to any distance?  The 100k is ~22 days away and I may be limping to the line.  Not exactly an ideal situation but the training and racing has taken its toll over the past year.  Given the configuration of the YUTC 50k, I will have the option of hitting aid stations every 4 miles which gives me a chance to drop if things get ugly.  I have never DNF'd and told myself, my body would have to quit before I did.  We'll see how this goes tomorrow.    Could I run the 100k without a 30 mile run tomorrow, yes but I have to see what is going on with my foot plus I had intended to do alot of walking anyway just to get prepped for the 100k.  Here goes nothing!