The race team is responsible for proving the displacement.
Yes, the SCTA is not well-equipped to do diesel engines via the spark plug method.
Best method, is that when you're building the engine, to get an SCTA inspector over and record the displacement and seal the engine, then record it in the log book.
Or, after you set a record, you pull a cylinder head. This can be problematic for some of the late model production V8's where it can be difficult to pull a head without removing the engine.