Water pump housing installation problems, Cracking at the block

[WH23G3G]

I finally figured out how my alternator brackets install. So I'm installing the water pump housing on my 400. I went to tighten the bolt for the top alternator bracket without a washer because of the heater hose pipe and once I tightened it it cracked around the threads at the block. Some pieces came off of the block. I stopped and took it off. Now I don't know what to do. Should I be using grade 8 bolts to install the water pump housing? I couldn't install the heater hose fitting with a washer on. Maybe if I use a thinner grade 5 washer it might work. But now there's a chunk missing of the threads on the block. Is there anything I can use to build it back up and maybe not tighten that bolt as much? Like some JB weld or Magnum steel. I'd to have lose this block and all this money over that little problem. I don't have the original water pump housing bolts. So I have to keep buying different lengths because I don't know how long each should be.

[BBKNARF]

I used grade 5 bolts and washers I also have 2 maybe 3 differant lengths they all stick out approx. 1/2" from the waterpump housing.
To fix the damaged threads I would use a heli-coil which most auto supply store carry like Napa.
You can also view it on you tube (how to fix threads with a heli-coil. Good luck