Heli-coil in a front cover bolt (SB)

I have a stripped thread in the bottom drivers side front cover bolt on a 360 block.This is a dead end thread that doesn't enter the crankcase at all.What I want to know is it ok to heli-coil this with the front cover on the motor.The drill size is 25/64.I have a spare block and it looks like there is lots of meat there.Thoughts?

Sure you can... you might need a bottoming bit to get
enough depth in the cover... IF you hit the block with
your drill bit just put some silicone in the back of the
hole just in case it were to seep anything
EDIT
your drilling the block.. correct.. if so measure the depth
of the spare block and the cover so you can drill that far
in and follow it up with the bottoming bit