I threw the ls1 idea out because I would have assumed 98-02 camaros and firebirds would be available? If your building a daily driver the ls1 would certainly be a viable candidate. My wifes camaro gets over 20 mpg driving it fairly agressively. It has 410 gears with a 6 speed. This is a 3300lb car that runs very strong. I wanted to use the engine and trans combo for my bird, until my wife saw it. Long story short I am in the process of freshening up the ls1 and a couple mods. I hope to have it back together and get some paint on it by spring. This would be a very very reliable strong efficient drivetrain. Too bad this is not a good option for you. If it is a car you are keeping, by all means you need to use what you are most comfortable with. My opinion may be different than others, but whatever powerplant you install can easily be removed for the original. However by the time you are done with the car the price of an engine is very insignificant in the grand scheme.