Tom, Happy to share. The links on mine are; 8" for the tool holder, 11" for the flat bars, and 6" at the tailstock end. I bought all the steel at Fastenal. They have a location close by me, that's why I went with them, but better prices might be found elsewhere. Here are some sizes I used;
Front and back link, 1" sq.
Flat bars, 1/4"x1"
Rear post, 1-1/4" sq.
Tube for rear post, 2"x.109
Base plate, 1/2"x4"
I have a Nova 1624-44 lathe without any added extensions, so I have a bed length of about 24". That's why I went with the lengths of links I used. You may have to adjust for your lathe. As far as bearings, the one's you show at McMaster Carr would probably work good, and it looks like they are cheaper than what I used. Mine came from here;
http://www.qbcbearings.com/BuyRFQ/Th...ring_TPS_I.htm
One other thing I did was using oil impregnated bushings in all holes. Got them from Enco, sorry I don't have a part #, but all holes were drilled to 5/8" and the bushings were 3/8"ID. I used bushings 1" tall for the square bar stock, and 1/4" tall for the flat bars. The bushings and thrust bearings added to the cost quite a bit, but I definately think they were worth it. Good luck building one of these, and if you have any questions, I'd be happy to help.
Rich
I had a Don Pencil Scorpion and Stinger hollowing system before building the articulated arm rig. I also had a Jordan 3/8 hook tool. All of these can be used in this rig because the Pencil system included reducers to allow you to use 5/8, 1/2, 7/16, and 3/8 boring bars.