New HD rim and spokes now in hand, so naturally it would figure that I was able to get the spoke popping issue resolved without them (so far). It's been about 60 miles of silence to date, so I thought I would leave an update. I purchased a spoke tension meter, and used that to even out the tension on all spokes. Most were actually high and they were brought into spec. Gave the tire a spin, and clearly setting the tension evenly was not going to be the answer. It was way out of wack.
Completely disenchanted with the tension gauge, patience hat on, and working a little at a time due to a sore back, I was able to bring the wheel back into alignment. Test drive showed it was still popping occasionally. Went to the tune by ear method, and after a couple of tries of tightening the "duds" 1/4 turn at a time, I ended up with a true running rim that ran silently - perfect!
I was told to use "28" on the spoke gauge for proper tension, and that does show near the center of the range of acceptable settings when looking at the charts. Early checks had some of the spokes set as high as 36. Final settings, the ones that will carry this 300 lb butt without constant complaining and breaking spokes, turned out to be 33-34. These are STILL acceptable on the charts I saw, though they are at the top of the "acceptable" range.
So my take away here, is that the spokes are going to need to be run a little tighter for the increased load I'm placing on them - AND - while tuning by ear sounds a bit crude to the uninitiated, it's actually a very effective way of adjusting spoke tension....
Silence IS golden!
Later, -Al