For your initial design you could also have chosen to use an additional byte to represent the type of the value. As representing the type would only require 2 or 3 bits, some bits will be unused (probably some more, due to alignment requirements), but maybe later on in the development of the compiler, those bits could be used to store some additional information. That would have made your code a lot simpler.

As you probably want to combine these valuse together into some structures representing the various language constructs, an additional byte to represent the type of the structure, and thus the type of its elements, would also be needed. Than you could do away with the extra bits representing the type.

I just think this is premature optimization and making things unneccessary complex especially for your readers who might want to learn something from it.