IMHO everything is possible. PIC will do more than those stupid unusefull 'stone age industry standard' chips. i can't remind how many Z80 and 8051 board based i upgrade with PIC. I replace those using a 'Mister's 8051 to PIC' adapter. BUT if you want to have a direct replacement pin-to-pin Atmel do some like the AT89C51

Since you know what every i/o do... you can't have any kind of problems.