Dura ace track hubs

On this topic, I might be need to space a Shimano freewheel out by a few mm.
I'm not yet sure of what wheelset, so can't test myself - will it be a problem getting that freewheel spaced out on a fixed thread?
Or will this be possible by the same width as with a fixed cog, which is about 3mm max, right?

Thanks

The teeth on a freewheel sit slightly further out than the teeth on a fixed cog so you might not need to space it out.