Engine Replacement

I have a 2023 civic SI that was in an accident. The bolts and mounting bracket that hold the engine block to the frame snapped rendering the block useless (unless aluminum welding is done). I was planning on getting it welded up as it is a very small piece however, after asking around the price of welding would be around 2-3k with proper workmanship and still it won't be up to spec. I decided on going with the engine replacement route however when trying to source an engine I encountered a problem, the 2023 SI shares the same engine as the regular civic which is the 1.5L Turbo however I wanted to make sure if it would fit and work with the SI as there is a large difference between horsepower.
1. Does the Si and regular civic engines share the same internals or are there any differences?
2. Is the horsepower gain done through the tunning of the engine or is it done through a larger turbo?
3. Would it make more sense to just replace the block (it will cost more because both engines need to be broken down)