In this update one more row of tiles is drawn at the bottom of the screen and the title screen is now full screen. Also, pressing Backspace disables the score box. This speeds up the game as can be seen at 1:58.
Download the game and the source code at https://github.com/FrenkelS/keensourc...

This is a recording of the game running on PCem v17 emulating a Tandy 1000 SL/2 with a 8086 8 MHz CPU and 768 KB of memory.