I would add a few things - you will have the VATS to contend with correct? I know my 95 Cutlass has it. So, if you don't have all the pieces for that (including the steering column ignition lock part) you will have to make/have made a computer to bypass the VATS.
Also - I had an 83 Regal that I put an SBC in. Even with 3.42 gears, I just wasn't happy with the performance or fuel economy, compared to a REAL turbo buick. Just remember that when deciding to go down this road of expenses. Trbo 668 is right - triple your estimates and prepare to pay that. This swap WILL nickel and dime you to death....