Welcome to CHR –

As mentioned above, lots of good folks here and a lot of experience. I’ll sound like a broken record here and throw my 2 cents toward a big block for your Cadillac. There’s a lot of BBC expertise here and Pat McCarthy will be able to guide you through a big block build.

If you do go SBC, I don’t think you dollar numbers are realistic. As Roger mentioned, there’s a ton of welding and pipe bending to make a turbo exhaust properly. I know the “wowzer zowzer” factor of a twin turbo motor is high, but the cost associated with building and maintaining one is also very high. You need top a drawer reciprocating assembly for turbo applications. I think $10K (or more) is likely what will be needed to do a twin turbo properly.

The SBC you referenced from Summit would not be a good fit as the compression ratio is 10:1. In my opinion, you need to aim for around 7:1 or 8:1 compression ratio for a turbo; anything above 9:1 you will have problems. You will need to run the highest octane fuel that you can find as the higher the octane the less likely you’ll experience engine knock.

Again, welcome and let us know what you decide!
Glenn