Personally, I would put the stresses on “found”, “no”, and “Tat” (though “tit” would get a little more emphasis than the other “unstressed” syllables). And as long as all the stressed syllables have the right timing, a limerick can certainly fudge the unstressed ones. I’ve also heard some, for instance, that put an extra unstressed syllable at the end of each long line:
There once was a maid in a tower
Who looked just as fair as a flower
Her hair was like silk,
Her skin smooth as milk,
But her breath made the bravest knight cower.