The problems are:

getting the correct claming force on the gasket and not crushing the fire rings by doing it up too tight (but thats just a case of using the correct torque settings on the new bolts, but dont assume they will be the same as the old ones!)

Weakening the block by taking more material out of it, but TBH this is the same for a helicoil anyway as you still have to drill it just the same.