Exactly. If the game don't ask you for a specific drive, then it's a very old game which prompt you for the drive a:\ by default.
In DOSBox, all the drives you mount are imaginary. It's only a matter of making the system think it's there. So, if you mount in DOSBox the directory (any directory) with the three files you specified as a:\, the game will be fooled once you run the install program.
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