Engine swap and running rich at idle
 

About 7 years ago, I swapped out a 1999 engine for a 2007 engine in B3000. The '99 was a flex fuel, whereas the '07 isn't. I just replaced the 3 cats, due to one melting solid and one gone, and it shows it's running rich, (-17 at idle and +6? after hitting 2500 RPMs), along with the last downstream exhaust sensor (replaced in August of this year) not reading anything. I noticed a rich fuel smell couple of months ago as well. The injectors are grey (not for flex fuel? I think the green ones are flex fuel.) If I change out the injectors to flex, (due to the computer reading them as flex) will that solve the problem? Or am I missing something? I'm waiting for the findings from the mechanic, I'll add more of what's going on, hopefully soon. Any advice will be helpful.
Thank you.