Just as an update, and since I've just successfully finished this conversion, too.....
Several things I found along the way:
1: The hole in the end of the Hex Bar is already 5/16" (at least on mine, a CB Performance set) - it took a piece of 5/16" steel dowell perfectly, so rather than tap the end for a shoulder bolt, I simply pushed in a 2" long dowell until it bottomed, then drilled a hole perpendicular through the Hex bar and dowell (about 1/2" in from the end of the Hex bar) for a 1/8" roll pin (often called a "tension pin"). Drove a pin through both and simply cut it off flush (used a Dremel and a cut-off wheel)
2: The Heim Joint I used (Aurora 5-mm or Sealmaster CFM-5) has a .3125" OR 5/16" ID hole in the bearing. Every so-called 5/16" bolt I measured was slightly smaller than 5/16", especially if the threads only went partially up the shank. That difference allowed the bolt shank to be quite loose in the bearing. Instead of that, I used a piece of true, 5/16" steel rod, and it measured out within .001" of 5/16" and made a much better fit in the bearing. This stuff is available in either mild steel (may rust) or Stainless steel (which will not rust).
3: Assembling the dowells in the ends of the Hex Bar and positioning the Heim joints such that you have approx. 3/16" of dowell protruding beyond each Heim joint WILL allow the rods (usually on the driver's side) to move sideways and fall out of the Heim joint. This has the added risk of potentially pushing a hole into one of your air cleaner elements (not cool). I suppose that really stiff springs could be used to keep it centered and in place, but I chose to use a couple of spacers placed over the dowells and between the Hex Bar and the Heim joints. I used a piece of 5/16" ID tubing cut from a kitchen faucet connection pipe (available at hardware and DIY stores) and used a pair of 1-1/2" long by 3/8" ID compression springs over the spacers to keep everything centered. I cut the spacers to allow about 1/8" of side play when cold, and it seems to be working very well.
4: I found that it's important to measure how high above the air cleaner base plate your current linkage is mounted. There were two holes in my CB base plate linkage mounting tabs. The lower set of holes allowed the arm which connects to the throttle cable to keep the angle of the cable correct for the delivery tube (which goes through the fan shroud) and doesn't try to mis-angle the cable and cause it to wear prematurely. If I were to mount in the upper holes (which I also found were of different heights on left and right on mine) I would need to change to a longer arm for the throttle cable to keep the geometry right. Mounting in the lower holes, however, gives you about 1/8" - 3/16" clearance of the hex bar over the alternator housing. Once you've determined the final height of your current Hex bar, then you simply set up the Heim joints to mimic that height in the new set-up. I moved that up a bit with the new set-up to provide more clearance for the alternator housing (I've now got 1/4").
I agree with Dale on time spent; this took about four hours start to (successful) completion. That includes an added hour to fix the problem of the left side falling out of the Heim joint. If I had forseen the problem, I would have done the spacers the first time and been done in three hours!! Once it's done, the throttle linkage is VERY precise at all throttle positions and is MUCH easier to "dial in" at both idle and 3000 RPM.
Well worth the effort.
gn
