Im no professional, nor do i have much knowledge at all in engine swapping, but what you say sounds like far too much hassle than it needs to be. Your looking to find the horsepower and torque an ls1 and lt1 gives out naturally aspirated, and plant it in a sport compact like an eclipse. Taking a 350ci and it's 6speed, and stuffing it into the front of a car normally housing a 122.8ci and a 5 speed tranny. Sure, getting the parts may not be hard, but the work itself is prolly harder than putting a 4g63 in a gs(as i've heard is hell in and of itself). But say you do finish this, and the car is operatable, AND your given the benefit of the doubt that the car can turn without fishtailing or any weight ration problems like everyone else has brought up, your still left with a 300 horsepower v8 in an eclipse. Weight difference between a 97 GS-T Coupe and a 97 Z-28 Coupe are 2970 to 3473 respectively, producing a 503 lb difference. The V8, being 2.85 times the size of the 4g63, makes up for a little of the weight difference. So i'd assume that your quarter-mile would be brought down from a mid-15 Stock GST to at best a low 13 with the 5.7l GST, assume all the above is correct and ideal. But, after all of this, all the money, the time, the patients, and the stress, your still likely to be slower than a slightly modified GSX. From what i hear, a few DSM have it sub 10 second quarter miles with the little 4g63. Overall, in my opinion, putting a 350 in the Eclipse is a waste, and if it's a loud rumble your looking for, put a loud exhaust on it, and your set. But then again, i may be wrong with a lot of what i said, it's my thoughts on it though.