I agree that an engine swap
I agree that an engine swap can lead you to a minefield of unknown modification. As an owner of a vintage car in NZ. An engine rebuild for my car was estimated to cost $6k to $8k, just for the engine work. That is with the engine removed and on the Reconditioners floor. Faced with this unexpected cost of nearly half the value of the car. I opted for a later model engine of the same design and manufacturer. However, I then needed to carry out many modifications to make it work. Improved performance and reliability are my goals.
Let's hope I am right.