How concatenate fields in SQL without losing data?

SQL Server DataTypes and Conversion and Concatenation
SQL Server 7.0 with SP3 in Windows 2000
 
I am working with 12 Fields.  I want to be able to concatenate the first 11 into the 12th Field.
 
Here are the field names and datatypes
1.)  [ACCESSION_NUMBER] [varchar] (12)
2.)  [TITLE] [varchar] (1000)
3.)  [AUTHOR] [varchar] (255)
4.)  [DOCUMENT_NUMBER] [varchar] (50)
5.)  [DOCUMENT_DATE] [varchar] (255)
6.)  [DOCUMENT_YEAR] [int]
7.)  [COMPANY_SOURCE] [varchar] (255)
8.)  [LOCATION] [varchar] (255)
9.)  [DOCUMENT_TYPE] [varchar] (255)
10.) [ABSTRACT] [text]
11.) [DESCRIPTORS] [text]
 
and the 12th field
12.) [SEARCHTEXT] [varchar] (8000)
 
The problem is I am converting the 10th and 11th fields into varchar(1500) fields.  This causing a loss of data. I can not increase the number since the character limitation on varchar is 8000.
 
I haven't been able to convert all the fields to the [text] datatype during the concatenation. I'm not trying to use a computational field, I'm running a stored procedure that would do the concatenation.
 
The stored procedure is:
CREATE PROCEDURE dbo.spSearchText
AS
UPDATE dbo.tblDocuments
SET SEARCHTEXT = ACCESSION_NUMBER + ' ' + TITLE + ' ' + AUTHOR + ' ' + DOCUMENT_NUMBER + ' ' + ' ' + DOCUMENT_DATE + ' ' + COMPANY_SOURCE
 + ' ' + LOCATION + ' ' + DOCUMENT_TYPE + ' ' + CONVERT(varchar(3000), ABSTRACT) + ' ' + CONVERT(varchar(3000), DESCRIPTORS)
GO
 
How can concatenate without lossing data? What Data Type should I convert all the fields too, before the concatenation?
 
Any help would be appreciated.
Thanks in advance,
Peter