I would say that as far as ease of upgrading later.......the engine harness is going to be (IMO, by FAR) the biggest headache. If you install a donor engine/harness now, and down the road you want to upgrade the engine to a new LS376, trying to figure out how to remove the donor harness and install a crate harness is going to not be a pleasant experience.
Other than that, if you're just planning on pulling the engine to do mechanical upgrades to it, this would not be an issue. The best thing you can do is plan ahead so that if you need to pull the rear sub-frame out of the car, you keep your electrical circuits back there so that you can pull the subframe without having to un-wire everything at the rear of the car.
__________________ Shane Vacek-VRaptor SpeedWorks, L.L.C. Supplier of Many Custom Products for the GTM! GTM's & SL-C's Custom Built for You! http://www.vraptorspeedworks.com
If you get above the 500 horsepower mark, then you will probably want to look at upgrading the trans to something like the Mendeola.
Like Crash says, stock and used.
if you don't abuse it, the G50 will move the car around. you can then upgrade later or rebuild it to cover the additional HP that you upgrade to.
almost all the parts are in the kit to use the G50. the nickel and dime stuff will add up if you don't plan.
Remember too that you are not limited to procuring your LS1 from a C5. Other GM platforms are wrapped around an LS1. They're usually cheaper for that reason alone. Your chances increase for acquiring it locally also.
You can always part out a donor, sell what you don't need and likely end up with a free LS1 with low mileage and your donor parts. I did this and bought a used G50 for about $3500 with all needed accessories. I rebuilt the G50 through G-Box for about $1500 so ended up with a pretty solid base package for $5k. As some already stated you can upgrade the ls1 pretty reasonably and get some additional ponies. Don't need much for a 2500lb car.
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