TBH buy a normal car. I made this mistake buying an import for my wife. She never boots it, it goes through heaps of fuel, and you cant get cheap insurance.
Support it partially with the exhaust. IMO it is usually the exhaust that causes the problem, imagine the force that an unhung exhaust puts on the manifold as you are bouncing along in a lowered car.
I also machine both manifold surfaces before fitting and whenever refitting if necessary.
I would just get a chinese one and mount the turbo and exhaust correctly, if fitted correctly they often last ages. Its when they get fitted with the weight of the turbo and exhaust hanging off it that they crack
I dont know about 26 cams being drop in, not on the motor that i tried, lost about 50% power all the way up to 5000rpm when we gave up and put the stockers back in.
I have dramas with my innovate, as i believe it is too close to the turbo, about 20cm. Interestingly innovate sell a bung extender/heatsink to alleviate this problem.
Stop putting $150 plugs in, they dont help. Either it is running too rich, which could be too much cold start enrichment, accell enrichment, or you have a weak spark.
The tuner should be able to tell on the dyno, just slowly increase boost until they become inefficient, or you make enough power. If it is a stock motor i wouldnt be going over 18psi