yeah this definitely needs to be done by a shop, or with a strong drill press at a minimum. When I replaced my heads I had them drilled out by a shop. I did just buy a nice used drill press for drilling steel. Makes a HUGE difference. I used to struggle drilling out 1/4" steel by hand with even good bits, but with the drill press drilling through steel is like drilling through wood.
1989 ProStar 190 with "Safe T Top", 351 Ford, GT 40 heads painted Ford Blue, Elec. Ign, 1:1, 720 hours, 4 blade prop, PP 6.5, removable platform brackets, custom color from factory, hot water shower, Boat Buddy & LED lights on trailer
2010 D3 Z7, 2 @ 32 off, 34 mph so far