Well, after a half day of cleanup, the culprit seems to be the battery box, at least primarily.
The hole in the side of the battery box, PS, where the J-hook fastens, had indeed become enlarged. That , combined with the smaller dimension of the Optima as was pointed out, seems to have caused the shifting of the battery backwards, allowing the retainer bar to slide down and make contact with the (+) terminal.
No paint damage, thankfully. ALso, as I was pulling wire out, I found that the convoluted tubing got most of the damage, not the wires themselves. I was tempted to leave them, but better to replace everything for peace of mind. ALso found that the Slee harness was NOT damaged, thankfully, but will be getting the newer (shorter) one anyway. If anyone needs the older, longer one, let me know...I'll ship it out.
Note the comments of Junk and Dan. Even using the battery spacer, shifting occurred. I'm going back with the same Optima (dual posts), despite the side post observations, simply because it makes for a cleaner attachment point for auxiliary stuff (lighting, primarily). I AM, however, considering the mil-spec terminals that some of y'all are using, since they seem to provide the needed room for ring terminals I need.
I did find terminal caps for side posts at the Marine SUpply store (that Rich mentioned) when I was there to replace the Kidde (B-C) extinguisher....a wise $5 investment.
SO...Words to the wise:
(1) Get a fire extinguisher. If you have one already, check the charge.
(2) Inspect the attachment point on your battery box.
(3) If you're gonna' use a non-standard battery, don't just assume that the bracket's holding it securely. Even mall-curuiser abuse might make it shift.