inp.start_pos, inp.beam_unit_vector, inp.beam_width_polynomial_coefficients, inp.particle_fraction should all be generated starting from information in the IMAS nbi IDS
I would also include generalizing for more than one NBI unit - this is slightly more involved than the beam geometry part alone but should be very doable!
https://github.com/ProjectTorreyPines/FUSE.jl/blob/05ec9438e5ad1220ea281850895efbf165f8d27a/src/actors/hcd/nbi/rabbit_actor.jl#L179-L184
inp.start_pos
,inp.beam_unit_vector
,inp.beam_width_polynomial_coefficients
,inp.particle_fraction
should all be generated starting from information in the IMASnbi
IDS