By processing Robin’s HD28305 data in ISIS without either calibration or instrument correction I managed to directly compare the result I got from IRAF. It shows they are in effect (and as one would expect) identical apart from small differences at the short wavelength end where my decision not to use a dark in IRAF is amplified by the flat correction. (As I understand it the 1 pixel shift in ISIS is well known)
This give me confidence in using IRAF and to make the next steps in wavelength calibration and then on to echelle spectra.
Regards Andrew