Since replacing the cap will require the block to be line bored, you might search for a shop that can competently perform that task first before you go down that road....
The engine builder that I'm hooked up with has been in the business for nearly sixty years and has the equipment to line bore. His Plan A is to have a 94 year old friend of his make me a billet end cap, Plan B is to acquire an end cap from an incapacitated engine and then line bore it. While I have a lot of faith in his Plan A, I'm actively looking for a Plan B just in case.
