How can a locate spatially the X-Shooter slit using the information presented in the header (in the "XS_SRE2" file)?

I'm trying to locate the slit from an observation available in the data archive ("XS_SRE2" file). I am trying to compare it with integral field spectroscopy data from another instrument (creating a pseudo-slit). For this, I need to locate the X-Shooter slit in the sky.

- Should I use the keywords "CRVARL2", "CDELT2" as offsets (along the slit) from sky coordinate ("RA", "DEC")? In this case, the Position Angle (PA) should be equal to: PA = - "HIERARCH ESO ADA POSANG" (note the negative sign)?

- The XS_SRE2 file has 99 rows (in the sky offset dimension). It seems that the first 33, and the last 33 ones could be discarded, since they appear to be an effect of the Nod&Shuffle technique. Is that that right? This is the reason why there seems to be a contamination (fake aborption) in some rows in the middle (34 -- 66 rows, mainly the extreme ones 34-37 and 63-66)? Also, if I want to the offset in the sky (along the slit) of the row 35 (e.g.), it would be: OFFSET(35) = "CRVARL2" + 34 * "CDELT2"? 

- There is a way to convert the flux units from counts to physical units (e.g. erg/s/cm2/A)?

Thank you,