I don't understand your contractor's problem. Maybe you should consider another one. I recently finished a bath replacement that involved a new tub and tile on the three wall surfaces. The tub is an American Standard Americast Princeton, and it has a lip on its three sides for overlapping cement board and tile. Go to the AS Web site and work your way in to the tubs (Trade Professional, Products, tubs, etc.). AS has great rough-in schematics that you can download with Adobe Reader and show your "possibilities limited" contractor.
: We are in the planning stages of remodeling our one and only bathroom. I would like to replace the old fiberglass tub-surround with an acrylic or cast iron tub, then add tile around the tub. The contractor tells me new tubs aren't designed to be used as tub-shower units and is suggesting a 3 piece tub-surround unit. The contractor says he is having difficulty finding a tub with the appropriate "lip" to tile above the tub. Any suggestions??? Thank you very much...