I would agree that an LS1 swap probably wouldn't be ideal for a first gen., but for a tt third gen. I think it makes a great choice. Here is a paragraph I took from the FAQ on Brad Hinson's site, just to add to the discussion:
How much will the car weigh? (Referring to a LS1 swap in a third gen.)
Answer) The aluminum GM LS1 and LS6 engines are extremely light power plants. With the complete removal of the 13B and the sequential turbo assembly, the project car's final weight is less than the total gross vehicle weight of a stock Mazda RX7. The final weight of the car is listed below. The car weighed 2,831lbs with a full Touring interior, sunroof, complete Bose sound system including the "Sound Wave," and a 1/4 tank of gas.
LF: 746 RF: 677 Total Front: 1,423lbs
LR: 675 RR: 733 Total Rear: 1,408lbs
