MK64 Portable 1.2
The race HUD and the menus are no longer stretched: they keep their original proportions, with the HUD anchored to the left and right screen edges and menus centred over the full-width backgrounds.
Install: unzip and drag the MK64Portable folder into PSP/GAME on your Memory Stick, then put your Mario Kart 64 (USA) ROM next to EBOOT.PBP. Upgrading from 1.0/1.1: just replace EBOOT.PBP; your data/ folder keeps working.