should i rebuild a 2ws 3406e or change to a 6nz c15

I have a cat 3406e 2ws that spun a rod bearing should i switch to a 6nz c15 or have my 2ws 3406e rebuilt

 

We did bad marks on crank #6 and the rod is messed up

 

Found a 6nz running take out with 300000 on complete rebuild for 12000 with paperwork 550hp and and they dont need a core

 

The 2ws only has 449000 original miles just baught in in Kansas Drove it back dropped a valve in #6 cylinder only 250 miles from where we got it .had it towed to western colorado back to our shop.had a mechanic put a reman head from cat in it bearings, and cylinder pack ,this was all in hole #6 rest of the holes looked great . so we decided to clean it the best he could and fix the one hole that was messed up and and put new bearings in. the only thing that we can think of that he did not get all the broken up piston and metal out and there was some still left in the crank. The mechanic was nice and felt bad about it and didnt charge us for the the labor or the cylinder pack .we baught the new head ourself and it is still good. Kinda dont know if its something wrong with the engine its self cuz we keep having trouble with that #6 hole. We do have a good rebuildable core with a good crank in it and the new head left. As far as down time we are a construction company that baught the truck for our heavy haul we still have our old heavy haul tractor we can use untill we get it fixed