Here are my PAL LowRes settings for 1350×1080 resolution that has 5:4 aspect ratio. Monitor needs to have 5:4 AR setting to get square pixels.
Since PAL 320×256 has 5:4 AR these settings will give perfect image for gaming with little bit of overscan.
240p/288p lineX4: On
H. samplerate: 1800
H. active: 1350
V. active: 270
Use H. and V. backporch settings to center the picture.