Unix has a tool called join that solves these kinds of problems for you. Given the following data files:

inbndtrk1.txt:
1:B&O:101
2:B&O:102

inbndtrk2.txt:
1:CSXT:1001
2:CSXT:1002

The following command

join -t: -o{1,2}.{2,3} inbndtrk1.txt inbndtrk2.txt
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B&O:101:CSXT:1001
B&O:102:CSXT:1002

Now, you can more easily format the results to whatever $client wants:

join -t: -o{1,2}.{2,3} inbndtrk1.txt inbndtrk2.txt \
    | perl -F: -ane'printf "%s %s | %s %s",@F'
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B&O 101 | CSXT 1001
B&O 102 | CSXT 1002

L-LL-L--L-LL-L--L-LL-L--
-R--R-RR-R--R-RR-R--R-RR
B--B--B--B--B--B--B--B--
H---H---H---H---H---H---
(the triplet paradiddle with high-hat)