itch.io

Yes, Gaplus was ported to the Commodore 64 back in 1988/1989 and was released as a budget game by Mastertronic. I have the tape original which the start of this video features the loading bitmap and Rob Hubbard's awesome tape loading music. 

This port of Gaplus to my general opinion is absolutely brilliant. The coders did a marvelous job porting the game to the much loved 8-bit computer. 

I guess the next step up would be a more faithful port of 1942! That would really test out a sprite multiplexer! That said, the larger sprites and attack pattern data would make it a tough challenge.