Your Briggs engine was made on 4 January 1984. Usually mower manufacturers build engines into mowers only a few months after the engine is made, but this is not a reliable way to date the machine. At one time I believe Scott Bonnar took several years to build out an overstock situation with Kirby-Lauson engines.

We do not seem to have a parts list for a mower with that model number. This is from the only other Colt 5 parts list we have:
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This is the version from the Colt 5-8 Owner Manual:

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Those are all we have. I'm told Colts are particularly difficult to document due to multiple versions existing.