Don't let the 'turbo stuff' spook you Phil. From speaking with you, working with you & seeing your posts, this isn't so much out of your league. Maybe just cause it's a bastard of a bunch of parts you're dealing with but from what I've seen of your work, if you can get the bits & get it together, the rest is easy.
My suggestion for what little its worth, swap the pipes & mani back to stock. Get it all looking A1. Leave the ecu, dump & injectors in place. Make the rest as unimpeachabley clean as possible.
Ok, here's the deal. With that tune & so on, that's a different issue, so leave it. Drive the thing for a few days & see if the DTC light comes on, drive like grandma k?
Then get it to the pit. No codes, runs ok bla bla. They look & hopefully dont know FPV's dont have 5" cats. If they drive it hard, it MAY throw a code? but might not too. In that case, you ask why they where driving your ute around hard enough for the light to come on? "wtf you done to me ute mate?"
Look, as long as the thing can run in vacuum without throwing a code, I'd say you're good.