I've been through six different sets of dual carbs over the winter and I can confirm everything else you've said is true. The chokes are different from XR to XL but it's just a bracket that can be switched, which if I read correctly you've already done. The 83 XL carbs have the different mixture screw that goes into the side instead of being on the bottom. I'm wondering what the ID number is on that XL carb set you found with the hex jets. The ID numbers I've found go as follows. The two sets of 83 carbs I went through were the PH60 and the rest I found were all PH68. All of those had the slot style jets. The XR600R carb set was numbered PH52 and that had hex style with the quick change bowls. The only other set with hex jets I found were the XR500R carbs PH50. Those had the quick change bowls that are interchangeable with the XL carb bowls. (That's not the case with the XR6 PH52 carb bowls. Those have a different pattern on the bottom of the carb body so the bowls do not interchange to any other carb set I'm aware of.) I found out about the XR5 bowls because both the XR5 and XL6 carbs actually use the same O-ring kit part number which means all seals are the same pattern. Nice thing is that you even get the big quick change bowl plug O-ring. BUT when I tried to put the XL carb bowls on the XR carbs they wouldn't tighten down all the way because they bottomed out on the longer hex jet. Maybe you could crank them in a bit further but I didn't attempt it. You can see how much longer they are in this picture. I've finished my 83 XL carbs with the XR5 float bowls and I switched them to hex jets. They actually poke out the bottom of the plug hole which with a XL bowl would be close to if not touching bottom.