U r pretty much stuck with the bill cuz of the car being black flagged at another dealer and the dealer that did all the testing might of worked with u until this. U could take legal action cuz of the pre diagnoses that u gave them but really is it going to be worth while, probably not. Being in the position r in I would get it in writing that your mods caused this issue regardless of what r intending to do. I would also press the issue of getting it covered under warranty firmly but respectfully cuz they did say that shouldn't be an issue so early. If I was in your shoes I would just get a built short block and be done with it and this $10-14,000 is ridiculous, do your research there r alot of good engine builders out there for a third of this cost good luck