which engine to replace mbn with 6nz or bxs tweaked?

New to here and would like some opinions. Give ya a little back ground info. mbn was running one of pitts tunes for last three years has borg warner turbo and a pdi exhaust manifold. Nothing against pitts when motor was set right it ran strong and was getting good mileage low to mid sixes. 2 years ago complete inframe new liners, reman head and rods and main bearings done from blown head gasket. They messed up liner protrusion told them what i wanted for liner protrusion and didnt do it set it to within cat specs. And head went second time. Cat repair shop put reman head on dec 9 2009 blown head gasket wonder why 2nd reman head overhead was set wrong and brunt valves. Been in cat shop four times in last year for overhead problems. Ecm even shut down motor because of high intake temps! poor power and mileage and now have spun main bearings so dont want to put any more money into the boat anchor. Thinking of either putting 6nz motor in or finding bxs removing intake valve actuators and replacing cam then putting my turbo and exhaust manifold and ecm on bxs motor which would be better choice on fuel,reliability and power and finally cost of doing such thing. Am done with Cat dealer repair shops.

 

Thanks for reply have parts from mbn. What would be safe boost levels with that high of comp at 18.1 think mbn is 16.1 was thinking about putting head from mbn on bxs motor do valve job on head then have liner protrusion checked at same time after this time cant afford anymore major break downs. Had one payment left on truck great time for this stuff to happen.