What was your process modifying that mold = size bits used etc ?
Using a square with the mold open, find the center of the gate at the head of the plastic and make a scratch on the mating surface at the edge of the mold...the very end of the mold. Clamp the mold securely I used two c-clamps, one to keep the two sides tight together and the other at 90 degrees to keep the sides level to each other. The mold went into a bench vise to hold it vertical for drilling. Using a 1/8" bit on a slow speed I drilled thru between the two side to the original runner just above the turn into the gate. I followed that with a 5/8" but drilling only about 1/4"....just making a pocket deep enough to let the nozzle end of the twin injector to snug up. Then a 7/16 was used to finish cutting into the original runner. After un-clamping and blowing the cuttings away I mixed up the high temp JB Weld and pushed it into each runner half on each side of the mold. When it was "just" setting I used a single edge razor blade to trim the JB flush to the mold face. When it was cured I went across the JB with a fine file as a touch up. Then it was injection time.
I did a few different injections using some old junk colors to see if there were any hidden glitches from doing the mod but found none and did the split color shown....again using re-melts. I did a number of single color shots as well using a standard injector. I have a 4 ounce Jacobs with a tapered nozzle and it shot just fine with the mod done as seen here.
Its actually a simple process as long as one doesn't try to force the drilling. The drilling took less time than the JB part of the mod.