In a word no. The N/A's have higher compression, smaller injectiors, smaller brakes and a different tranny. Generally it is more to buy a N/A and upgrade it to the level of a stock TT, than it would be to just start with the TT. See http://www.suprastore.com/iamlookforsu.html for more info.
you meant buy a single turbo Supra SE then upgrade it to twin turbos? Anyways, unless you spend a lot of money, you won't be able to reach what Twin Turbo Supras have. It's easier to go with just Twin Turbo in the first place if you want a fast Supra.