It depends on what I'm doing, but I have been successful at just randomly putting two holes in the metal piece, place two short pins, of the same length, with sharp points on them in the holes, and then pressing the handle material to them. Gives you two marks to drill.
You could even do just one pin first! Get it drilled in the handle material. I go .150 in the metal,
.400 in the handle. Place the full length pin, .550, in place. Put another short pin in the other hole, slide the two parts together, because they now have one full length pin to align them, and then make the second mark in the handle material.
There's no "spacing" or measuring.
Get creative, use your head.
(Then there's the "secret" way, which I can't tell even at gun point!) But the above works great.