I have been doing this by hand ... (which comes with it's own challenges - so I'm open to easier methods)
A few tips;
1) Look at code currently use in Lazarus Pascal units
Quite a few functions etc already have been implemented - you may have to do a search on file content. The forum has some examples as well.
2) Don't forget to link frameworks (you can find the available frameworks here: /System/Library/Frameworks/) eg.;
{$linkframework foundation}
{$linkframework applicationservices}
3) Take a look at
this topic when you want to "import" a .h file.
4) Some of the items used, are initialized by default (no init needed), some are not (init needed). For example NSFileManager has "defaultManager" initialized.
But all in all it always takes me quite a while to convert, try and learn about the functions I use.