Apparently, you have done the modification to lower the position of the IFR's in the metering block. Did it make a noticeable difference in idle quality?Drilling/threading lower hole IFR in the meter block does not accept the flanged brass so #6 set screws is a necessity.
It’s true pre drilled brass is a whole lot easier to achieve desired finished hole. And solid 3/16” brass #6 set screws will require a larger C-bore prior to hole drill so the thickness of the hole depth is not too thick. The flow thru the C-bore may affect flow but it can be filed off flush.