Back in the day I used the simple DfmToLfm converter here to convert Delphi forms to Lazarus forms:
http://wiki.lazarus.freepascal.org/XDev_ToolkitThe idea is that I would only make form design changes on the Delphi side, then convert the forms whenever I wanted to test with Lazarus.
This also provided a way to correct some LCL deficiencies on Mac, specifically to substitute a Mac font instead of the .dfm font. And also to set some controls' TabStop property to False so that tabbing skips over controls that cannot receive focus on Mac (TButton, TComboBox, TRadioGroup, etc.).
Surely a simple converter from .lfm back to .dfm would be possible too.