It discusses TP 3.0's operation, supposedly based on a disassembly. It's less interesting than it sounds (it's mostly a high level overview of how a small compiler works, rather than a real study of TP internals), but it helps.
You might also be interested by what appears to be a perfect decompilation (leaked source code?) of the IDE of Turbo Pascal 6.0 written in itself using Turbo Vision and the internal compiler/assembler/debugger : go to http://www.exmortis.narod.ru/index_eng.html in the "Compilers" section and search for "tpascal.zip"
It discusses TP 3.0's operation, supposedly based on a disassembly. It's less interesting than it sounds (it's mostly a high level overview of how a small compiler works, rather than a real study of TP internals), but it helps.
Long TP discussion thread with dead link here: https://news.ycombinator.com/item?id=10202299