Modification of PV list

Hi

I am attempting to modify the below PV list, which is a lookup on the number window in the payment application screen.  I want to include a column in the PV list called Credit No.  This field is a custom field taken from the SOShipheader.user8.

Could someone point me in the right direction. Below is the procedure for the PV list but I do not know how to add that field in the columns.

Any assistance will be greatly appreciated.

[ARDoc_CpnyId_DocType_Cury_Ref3] @parm1 varchar ( 10), @parm2 varchar ( 15), @parm3 varchar ( 2), @parm4 varchar ( 4), @parm5 varchar ( 10), @parm6 varchar (10) as
    Select * from ARDoc where
   CpnyID like @parm1
   and CustId = @parm2
        and DocType = @parm3
        and CuryId = @parm4
  and ((ApplBatNbr = @parm5 and ApplBatNbr <> '') or (ApplBatNbr = '' and Rlsed = 1 and CuryDocBal <> 0))
  and refnbr like @parm6
  order by CustId, DocType, RefNbr