Chain rattling in lowest gear despite adjustment
Assuming you haven’t done so, I’d check that the derailleur moves freely and isn’t seized or gunked, preventing it springing inboard up against the low limit screw. You can peak at the screw tip to check.

Drip some oil in the pivot points and maybe spray light lube carefully on the mechanism, then exercise the FD manually with your hands a number of times to make sure it is moving freely. (No chain movement or cable tension). 

It's worth measuring the chainline too and reporting back to ask if it’s in spec. for the B.B. spindle length possibility. 

It might be that you can tweak the derailleur so that it isn't exactly parallel, but functions properly, i.e. no rubbing, shifts properly and doesn't drop the chain inboard or outboard from the chainrings. Try rotating the tail of the derailleur inboard just a little and see how you get on.