Computer swap? Aftermarket?

In general, if I have a 4.3 Vortec V6, 2001 or newer model. Can I take the computer from another vehicle with the same engine, but possibly a different year (still 2001 or newer), and use it with my engine? Also,
does anyone sale aftermarket computers? Links to any on-line?
I may be getting an engine from a 2005 Silverado, 1/2 ton, auto tranny. It doesn't have the computer though, but the guy said he would give me one which I think was from a 2001 S10 Blazer, also with auto tranny. It may have been from something else, because he has 4 or 5, but they were all 2001 or newer with 4.3 engines.
I'm going to be using a manual tranny in my custom rig I'm building, so does it matter if the computer was made for an auto? From what I've been told the same computer runs the engine and the tranny, so will it be a problem that the tranny sensors will not be hooked up?
I understand the computer will need to be reprogrammed no matter what, when moving from one vehicle to another (I guess unless everything was exactly the same, including tire size, gears, etc). Is this (the reprogramming) going to cost me closer to $100, $500, or $1000? Assuming I get all of the wiring correct, or maybe install a Painless wiring harness, and then just have someone do the final programming for me.
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The computer and harness will have to go with the year engine you are buying unless it is the same year and trans. switching transmissions will require a complete reprogramming.

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Thanks for the info. I'm going to wait it out a few months and try to get a complete engine from a standard trans., with computer, and other parts. Kind of morbid waiting around for someone to *wreck* the right vehicle, to get the parts I need.
Shep wrote:

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