It does run terrible because you've given it no ability to run properly. There is absolutely no good reason to keep those injectors in there, it isn't going to run properly without a useless tune. The NA injectors are the same as 240sx injectors and can be had for around $20 for a full 240sx fuel rail. I have half a dozen spare rails with injectors in a bucket in my garage for just that purpose. You should not spend more than $100 replacing the injectors.
Cheers, JBrobst
"A life spent making mistakes is not only more honorable, but more useful than a life spent doing nothing." George Bernard Shaw