Hard to answer. The ST-300 1st gear is a pathetic 1.765. That's almost like the 2nd gear on other transmissions. But your top gear is still 1:1. So it all comes down to how much RPM you're willing to deal with on the highway. It really is a lousy trans in that respect.
BTW, no one says you have to throw the trans out if you're not using it. You can install a 2004R without resorting to cutting any virgin sheet metal. If you're willing to put on non-numbers matching components like a 4bbl setup, what difference does it make if the trans is correct? Swap it back when you sell (or include it in the sale) you can still call it numbers matching.
