I saw someone mention somewhere that there was a spacer that could be bought so you could use the tapered bearings and adjusters. I havent seen one, but I'm sure it wouldnt be hard to make. Just hard to keep in place when an axle was pulled... There's nothing in the centersection to retain anything...lol.
Use a little heavy weight grease on the spacer...holds it in there just fine. I've never seen one come out just by pulling an axle.
Nothing wrong with green bearings if you are driving it as a cruiser. Now if it's an everyday driver or you are going road racing, the original roller bearings will long outlive the ball bearing "green" bearings...they are good for about 30-35K miles from what I've seen.