Always precisely read application notes, documentation etc. All the compilers have their own dialect nuances and you can't expect that, say, Keil sources will run on SDCC out of the box. Usually the parsing to make the sources compilant with the new compiler is easy and can be done by hand, sometimes you need to write a parser i.e. in Perl.

As to simulator - I can't quite believe the clocks don't work. Do the manuals say so or is that just your code being buggy? (not once I was fumbling "stupid compiler!" then checking the code for 10th time and finally slapping my head "It didn't work because it couldn't!" - a typo like missing a # or writing JNB where JB should go is all too common.