Quality 54 inch tub

Hello Folks,
I have a real problem. I am in need of a 54 inch tub for a bathroom remodel, but have only found 5 models.

2 are porcelain on steel
2 are ultra tuff/armour plus (assuming similar to americast).
1 is cast iron(kohler), but has no tile flange so it does not seem as if it was intended for use with a shower.

I have found nothing else and am skeptical of americast and porcelain on steel. This is going to be a quality remodel, and I want it to last.

Any ideas or opinions are welcome. Thanks.

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The Kohler Seaforth K-745/746 is a cast iron tub with a tile lip.

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If it was for me I surely choose the cast iron.........

The problem with the Kohler is that it interior dimensions (according to Kohler) are tiny. In fact, they don't make a whole lot of sense to me. How does a regular tub go from 48 inches to 37 inches in length in the bathing well? That's an 11 inch differential. I would imagine there is a large slope in the back area. Anyone know? I have no preblem spending the dough(it is an expensive little tub). Just seems like very little for a lot of money.

I just check my old Kohler whirlpool. It is a 5footer. Only 38" length for bathing well(lower). Is this typical of Kohler or all tubs?

AquaGlass makes a fiberglass 54" but I am not crazy about the quality. I have the same problem that is why I am considering a roman tub. All of the 54" that I found (which was very few) were so darn shallow. Good luck in finding a good one.