If you're doing them by hand, an NPT ream is a life changer. They're kind pricey for a one off, but they make all the difference. Gives you the taper, so you're just cutting threads in that, vs digging in deeper and deeper as you go.
https://www.mscdirect.com/browse/tn...eamers-Sets/Taper-Pipe-Reamers?navid=12106203
