Ok heres the situation at hand. I know someone who has an 89 RS Convertable with a 305 TBI. He is mulling some options as to what to do engine wise. The 2 choices are a Gen1 SBC (most likely a 350, maybe a 383) or a 5.3L Vortec out of a 03-04 avalanche. There are guys on a local car enthusiast board who are all for the 5.3L Vortec just because its related to the LS1 and they are thinking its going to make great power and good economy (I do not doubt it) but I think they are failing to realize whats involved with the swap (the wiring, the mounting of engine, transmission situation) I don't know, I've only done 1 swap (v6-v8 in my 84 sport coupe) and it was kind of a headache for me because even though I spent hours and hours reading on thirdgen, getting the actual work done and understanding everything that needed to be changed kinda got over my head, since I was a noob back then. I'm saying he should stick with the Gen1... yeah it won't get the glorious gas mileage but its not like it'll be TERRIBLE in comparison, especially considering the hp output/potential. So I'll appeal to the thirdgen crowd, ask what you guys would do. I know plenty of guys here have done both swaps... keep in mind that cost is a factor and I'm guessing so is downtime.

What are the goals for the car and what is the budget? If you only drag the car and drive it on the streets from time with a limited budget I would go genI carb. If you have a little more money, know how, and have to drive the car a lot there is no question that the 5.3 GenIII mill would be my choice. You can get those motors for under $900 now (complete with 40k miles or less). Granted there are the normal Gen III swap requirements (motor mounts, tranny, tranny crossmember, wiring, etc etc) but if you want a reliable 300hp and 25+ mpg in a 3rd gen that is hard to pass up (assuming you are willing to go through with the swap). If you keep your eyes peeled you can nab a 345hp 6.0 iron Gen III for the same price. In a 3rd gen platform the Gen I is still the best $ for hp but the Gen III mills offer so much more than power alone.

I voted Gen III because I would like to see what they would do in a third gen.But then again you go back to what Shifty said