I am really with Scott on this one. If you want a fast car, get a fast car (see signature line). There are little things you can do like the things that you mentioned to get a little extra out of it (you didn't mention blocking off the vacuum lines to the passenger side of the engine). I have already replaced one cylinder head and don't care to do it again.
But, if you want to fantasize about what is possible, and can read dutch(?), then check out this
That is somewhere around 400HP, but notice that the a/c is gone.
\'87 Mer-B 300D (220,000 miles) (sold)
\'93 Mer-B 300D (173,000 miles) (sold)
\'87 Porsche 928 (101,000 miles)
\'98 Dodge Ram quad-cab (250,000 miles)
\'2001 CLK430 Cabrio (50,000 miles)
Past cars: 1969 mercedes 250, 1981 300D, 1972 220D