Not likely to be anything close to pin or code compatible.
Why 8-bit? Consider 32-bit STM32 Cortex-M0(+) type parts with more and current tool availability. Free Keil, free GNU based
Consider STM32C0 and STM32G0 families. Write in C, and port over application
What OTHER requirements do you need, size of FLASH perhaps doesn't directly correlate? Might indicate code complexity, 32-bit might do some operations more efficiently, good use of subroutines, and optimization can also help.
