2000 Cherokee Sport 4L 95K,

I have completed work on my front end and in the process of replacing my
rear shocks.
Of course the rear upper bolts broke off.
This newsgroup had great advice regarding a repair by drilling thru the rear
floor and installing nuts and bolts.(there was a nice link to a homepage)
Before I try this I would like to know if anyone has had any luck with a
tap.I have drilled out the bolts and the stock bolts are now a bit to small.
The bit was 5/16ths. Is a Helicoil strong
enought to use ?