success - thanks to this group once again! I had to play around with the type of script. it was a Post-Read on the SO Header table but it worked. The SO Header History now has a UDF that matches the SO header Ship/Expire date. The SO History Inquiry displays the Ship Date UDF. Happy customer! such a simple script in case anyone else can use it.
odate=""""
retval = obusobj.getvalue(""ShipExpireDate"",odate)
retval = obusobj.setvalue(""UDF_DATE_PROMISE$"",odate)