This thread has veered off from the OP's question . . . so, in an effort to continue this discussion
, the above linked BHE 28/.410 bi-gauge set was listed by RHO over a year and a half ago along with another BHE 28/.410 that has since been sold. Both of these were shown on PG. 2 along with a couple of equally as rare and even more valuable 28/28/.410 A-1 Special 3-bbl. sets in this thread:
https://parkerguns.org/forums/showthread.php?t=34810