Fuel injector inserts made for Kia lower intake. THis will give you a general idea of how i did it. This is the brass fitting a used to make the insert. Its a 3/8 pipe thread reduced to 1/4 pipe. The 3/8 pipe fits right in the injector ports in the manifold. So what i did was is round off the hex part of the fitting to where i knew i could press fit it in. And use JB Weld to keep it sealed and in it home. I used a step bit to open up the 1/4 end of the fitting just till the injector O Ring fit in it decently. The step it makes a very nice step action in the fitting so its impossible for the o ring to fall further in.
Bad pic but all i have. Ill make another for reference.
Now just Round off the hex and press it in.