This can be achived with the help of the sequence number.Create the sequence number for the each record in the first file and the second file.then select the required data(345,654) from file one and required data (678,567) from the file 2 based on the key value(ie..sequence number).
you will then get a file with the data like below.
then use this file as the filrst file and your 3 rd file as the second file and follow the same procedure to create the final file.
The DFSORT/ICETOOL job below will do what you asked for.
Since the input files have RECFM=VBA, the data you show actually starts at position 6 (after 4-byte RDW and 1-byte cc), so I've adjusted the starting positions accordingly. I assumed you didn't want the cc in the output file, so it would have RECFM=VB and LRECL=21. You can change the job appropriately if those assumptions aren't correct.