Making those kinds of countersink bits in silver steel on a Myford is fine - done it plenty of times myself. The biggest issue is machining the half-diameter; you can file it, but I used my Myford milling slide to machine it. Even easier if you have access to a milling machine. If you make a slight undercut just where the cutting surfaces meet the full diameter, you end up with a flat surface that is easy to touch up on a stone if needed. Hardening is one of those odd things that sounds very difficult and technical but is actually very straightforward when you do it. Main thing, as Mekanik said, is to heat the shank. not the tip, and watch the colours travel towards the cutting edges, but don't use too much heat as the travel can be a bit too quick. If that does happen, you can always try rehardening (cherry red and quench) and then have another go at tempering. Silver steel properly hardened and tempered actually cuts mild steel surprisingly easily; what it can't take is heavy/fast cutting which overheats the cutting edges and destroys the tempering. That's one reason HSS was invented - holds its temper even when pushed hard.