Also what is the standard step down size recommendations for metal drilling?
Make sure it is a machined, balanced pulley and not the cheap cast ones.
Agree, a good recommendation if one is turning it high RPMs, but for slow speed metal drilling, he'll never notice the difference. (Yes, the motor pulley is always turning 1750 RPMs, but revving the spindle up several thousand RPMs will emphasize any out-of-round or out-of-balance in the drive pulley. The belt chosen is as important to smooth operation as the pulleys.) I've used the hardware store Congress cast aluminum pulleys successfully many times.
As to the "standard step down" there isn't one. It depends upon the drill diameter chosen and the metal being drilled. There are several charts available on line which give diameter and RPMs for different metals.
The "DP 220" is a nomenclature misnomer; actually that's the head casting number. Yes, many use it, but there are parts and info to be found by a search for Delta 14" and Rockwell 14" drill press.
jack vines