165mm steerer tube on fork but headtube length is 120mm , stem is 40mm is there a really low stack headset to allow this to fit the frame?

What sort of headset does it take?

Headtube is tapered

You’re going to be pushing that… even fully internal headset is going to add a few mm of height.
As above need to know what sort of headset it would take, just being a tapered head tube it can still be internal/integral/external etc. There are 30/35mm stack height stems about.