I recently moved and got my looms back from friends who stored them for me. It has been at least 20 years since either one got more than a superficial dusting. Since my floor loom is already disassembled, I figured that this spring will be a good time to get it really cleaned up. My previous weaving space was in the basement. Now it will go in a much nicer spot in the family room. I want the loom (a Newcomb Studio Arts 4-harness) to look like furniture rather than something that belongs in a work room. I read through the posts here and in weaver's blogs for advice and got enthused about the whole project.
However, the weather in April was not cooperating for a big project outside or in the garage. I decided to start by cleaning up my Structo wooden table loom. It started off in good shape and my major goal was to add more heddles. Thanks to Deanna Baugh I had 200 new heddles to add, giving a total of 109 per harness. I downloaded the manual from the all_things_structo Yahoo group and looked for directions. It says to unhook the harness from the lever.
Okay, that is not too hard to do. The photo shows how the harnesses attach.
This is how the harnesses sit after they are released. There is a wooden cross piece under the harnesses with a rubber pad at each end. There are five metal pegs that separate the harnesses on each side. The clearance at the top is not enough for the harnesses to tilt to the front or back to slide out. Unlike the simple method shown by Sally Orgren, these harnesses don't just come out the center. I could not find any photos of how to take apart a Structo 600, so I took these. At least if I got stuck I would know where everything came from.
My first hint was to remove the castle. But where?
The bottom metal bracket looked like a good place to start.
Taking precautions: 
After removing the screws on both sides of the castle, the metal bar that connects the front and back beams must be gently moved to the center.
Once that is done, the castle lifts off and the harnesses are free!
I polished the wood with Howard's Feed and Wax. The finish was in good shape so there was no major change in color. It is now clean and glossy. The metal had some spots where the paint was chipped and rust had started. The only really bad section was the metal bar that supports the beater. That was clean at the ends where the beater protected it, but rusty everywhere else. Emory cloth (150 grit) with 3-in-1 mineral oil took the rust right off. I used fine (001K) emory cloth on the spots that weren't so bad.
I tried a couple different approaches for cleaning the reed. It has 9 dents per inch and was showing minor signs of rust. The emory cloth and oil method worked alright but was very slow and left the tines covered in rusty oil. Going back through them with a paper towel was even slower. One of the weavers here recommended bike oil as a lubricant, so I got out my bike clean and lube kit. The CyclePro Miracle Metal Polish was just the thing. It says it removes rust and tarnish and protects bare metal. It certainly took off dirt and tarnish with much less effort. The reed does not look like new. Maybe if I had more patience for the wiping down each dent that would have happened. I would rather put a practice project on the loom to clean off the residual stuff in the reed.
Threading the new heddles on the harnesses was slow but much aided by Sally's advice to keep them in order with strips of thin cardboard. 
I cut strips from a package insert to be just a bit narrower than the harness bars. After sliding a strip into the holes in the heddles (still on the harness bar), I taped the ends together. This worked great. The process would have been very quick if I had not been counting them as I was putting them on. There was a note on the loom when I bought it saying that it had 58 heddles per harness. That was pretty close. Now I have enough to weave the full 20 inch width of the reed at 21 epi.
I really appreciate all the advice I found on the web and I hope that these photos may help other Structo wooden loom owners in the future.