<sarcasm>Thanks for all the help.</sarcasm>
As info, I do not believe anyone makes a pan with no threshold. I
searched the internet for days, and consulted with every plumbing
supply house within 25 miles of here. No one had ever heard of such a
thing. The closest I got was a custom made cultured-marble pan, which
was $400 and 3 weeks, plus 2 more people to install because of the
weight. Also, the marble pan had no flanges, so I was concerned that
it would leak if the bottom tile joint ever failed.
After completing the demolition, I found that a 42x36 fiberglass shower
pan fits perfectly. Rather than trying to build up the threshold with
tile, I plan to build up the subfloor beneath the pan so that its
threshold is at the height of the original curb. The old glass
surround should go back in just fine. No chance for leaks with this
solution, as there will be no horizontal fiberglass-to-tile joint any
longer. The new tile backer will extend about 20 inches above the pan.
My only complaint is that home centers don't stock 42x36 pans. Since
it special ordered, it costs more than twice as much as the 36x36 pan
that's in stock ($196 vs. $91). And, it take two weeks to get it.
As an aside, while investigating the adjacent wall cavities for rot, I
found a beer can someone had left there. Perhaps this is why my old
shower leaked. Seriously, from what I have learned recently while
considering putting the tile shower back, I don't see why anyone would
want one. You have to do all 50 steps of the installation exactly
right. Get any one of them wrong, just a little bit, and the thing
will leak. No thanks.