Hi,
Ideally Vendor Name should be populated from LFA1 & not from BKPF.
Fetch the Vendor Name Details from LFA1 - Name1 & Name2 field and yes it is possible to concatenate both and could be printed in the Cheque Script/Form.
Would advice not to use the Text Field for Cheque Printing as it could be changed even after posting the Payment document.
Regards,
Jaymin R. Bhatt