Hmmm ... This might be a possible alternative to replacement or re-enameling that old tub. ReBath simply drives up to your front door, rings the bell and as quick as "zip-zip" installs a new liner custom molded to perfectly fit over your vintage tub (mine is "Arcadia").
According to their site, ReBath uses exact duplicates from an inventory of over 1,000 bathtub molds. Since they are using the same bathtub you have in your home to make your bathtub liner, they say they can guaranteed a perfect watertight fit for your tub or shower. They don't even need to remove your tiling. How cool is that?
*zip-zip quoted from the Chief of the Future, The Honeymooners, Episode 7 - "Better Living Through TV" ;)