Thanks for the replies...good info..When I said "machine shop" in my original post, I was simply at a loss for words.  I wouldn't actually use a machine shop, but rather a good welder, or most likely just do it myself.  Thanks, TXCutter, I didnt know RollACone did that, but should have..

Plowboy is correct, there is no doubling-up on the rockshaft since it is solid to begin with.  On some 610's, JD actually tried using the hollow shaft (again), much like they tried on the 1600.  Needless to say, it was a big flop and JD eventually came out with an "update".  One of my buddies still has (3) 610 [junker] rockshafts sitting outside his shop in the scrap pile.

Boetboer:  At the very bottom of this reply are a couple of pics of my wheat sowing setup.  It is certainly nothing fancy, but it does a great job at getting wheat up.  The tractor is a JD 8760 (it now has about 4200 hrs on it), the plow is a JD 1610, and the drills are JD 9300 hoe drills w/AcraPlant tips.  The drills have a transport system which allows a person to raise them up, and pull them long-ways down the road (long instead of wide).  The drills hold about 3 bushels per foot (40 feet wide, for a total of about 120 bushels).  I know that the commodity carts hold a lot more seed than this, but I can still get a fair amount of acres planted before having to re-fill.  We usually sow around 36 lbs per acre. (+ or -, depending on what time of the season we are sowing.  If it gets really late, we will bump up the rate a little bit)
I took these pics today.  I guess you can tell how muddy it is in the field right now!  I did not put the covers on the drills (you know--"only a 20% chance of showers"--ended up getting over 2 inches (and a LOT of hail) at this place), and I was afraid that the seed cups were going to bridge-over/stop up, so I went out there and turned the seed cup driveshaft with a wrench and emptied the seed cups.  On these JD drills, the seed cups will get rained on, sometimes, and the grain will harden-up in the cups.  If a person does not grind that seed out of there, one might have to empty the drills completely in order to un-stop the cups.  I didn't want to chance it, so I made the muddy excursion out to the drills and ground out the seed cups.

(BTW: a while back, I had 30 ft of the same kind of JD drills.  I filled them up, completely, one late evening so I could get an early start the next morning.  Well, sure enough, it rained BIG TIME that night and I did not go to the drills for a few days.  A few days later when I did go back to sow wheat, the seed had hardened-up in the seed cups.  It was so bad that I could not grind the seed out.  Also, the moisture had "traveled" up the seed cup, into the drill box and each cup had a hardened "plug" of wheat at the top (inside) of the cup.  Needless to say, I had to scoop the drills out (by hand w/ a gallon bucket) in order to get that slug of wheat out of the very top of each cup.  It was a huge pain. I threw each gallon back into the truck so I could later put it right back via the 12v auger (no gravity wagons at that time). If I had just gone over there and turned the seed cup driveshaft, all of 'that' could have been avoided.  Oh well--you live & learn !!  If I had it to do over again I would stick a hydraulic auger in the drills and get a lot out using that method..)