Camry+Celica?, camry engine? Options

[monkeywrench]

Hi, I'm Lea (Lee-uh) a 17 year old girl, and car nut.

I'm going to be getting a Celica soon (possibly buying back my moms old one) for really cheap (just wait, I'll explain) and I don't care what's up with the engine, I'm going to pull one out of a junkyard and have it rebuilt. I read the topic about what engines will and won't fit. From that list I'm leaning toward the 3S-GTE, but id wondered about the engine from a. '04-'06 Camry (a 3MZ-FE V6). I don't know if this would fit in the engine bay, or if I would have to get a new transmission along with that. Or would I be better off finding a 3S-GTE? I want something more powerful than a 7A-FE or a 5S-GE.

I'm still learning and don't know much about interchangeable parts. Also, about how much would it be if I had a new transmission installed in a '94 ST coupe?

[monkeywrench]

Where would I find an ECU? My dad thought he had to replace the ECU in my moms old celica and he went to the local Toyota dealership to order one and they said ECUs for that car aren't made anymore. I've heard the ECU out of some other cars would be the same as from a Celica?
And arent the chassis codes for the USDM ST and GT AT200 and ST204? Are those the chassis codes for all the US 6th den Celicas? I was wondering because before I buy a Celica I want to know what the chassis code is.