first thing as sultan said is the ecu
get that first and go from there. you have to remember that the ECU doesnt give two shtts what motor it is controlling. it measures and controls accordingly.
a correct and propper tune wil actually put less stress on your internals while giving you an increase in power through efficiency alone.
the non turbo head gaskets could be an issue tho, but the compression can be compensated for in the tune.
me i would sort the brains and fuel (pump, injectors, reg etc) together, along with the usual exhaust intake mods etc etc etc and leave it as is.