ISX cm871 in frame overhaul nightmare

[Derf]

Hello all, new to this forum and this place is heaven! for now..
Currently working for an oil field company in northern Alberta, 4th yr apprentice heavy duty mechanic. I've worked my way up the ranks these last few years to finally doing my first in frame overhaul! Yay.. I've done a few head gaskets, and tons of diag around these engines with the help of EDS, and of course Rawze /Youtube videos (Thanks man)

The story begins with a customers truck being towed in with oil in the coolant. well of course I went straight to the oil cooler and found it to be defective. The shop manager (also a certified cummins tech/long time wrencher) talked the customer into checking the head gasket as this particular truck was pushing exhaust gases through the cooling system way before the oil/coolant mixture started happening, so he says ( I never seen it with my own 2 eyes). Seems to be pushing gases through #3 hole past the fire ring to a coolant port in the head gasket ( I believe him now). Of course with the head off why not check liner protrusion, #4 measured at 0.006" and the boss man called for an in frame.. Our shop had built a cylinder liner installer tool to clamp down the liners for measurements, works perfect on single over head cam engines. But this double over head cam engine the tool does not work for cylinder #1 ( part of tool hits front gear housing ) I highly suggested in getting the proper tool for the shop but my manager just told me to shave off part of the home made tool and make it work, so I did. Unfortunately what happend was i thought i had the tool fitted exactly to measure #1 liner protrusion and rammed the head bolt down to clamp the tool to liner. Well i stripped out a headbolt hole in the block ( Ifuked up big time).. I removed the tool and just started regretting every decision I've done to this point.. So after chasing the threads ,I measured exactly how much threads i damaged and found that with the cylinder head and head gasket installed the head bolt will have 1/2 good threads and the other half will be damaged. It's the #18 hole when doing the head gasket torque sequence.
After installing some shims and doing a test run with the head bolt and damaged hole I found tht i could do the 300ft/lbs PLUS the 90 degree turn, I was told everything should be ok..
Well I am still a little sketched out because ya it holds but will it hold under hi compression?
I found a Heli Coil insert and tool online, wondering if anyone has ever used it with success?
(M20111-70 Headbolt Hole Repair Fixture Service Kit Add On For Use On Cummins ISX)
What are some ideas that I could run by my manager to allow me to fix my mess up?
Thanks