Bootloader compatible?

Can i use arduino bootloader for Atmega1280 on Atmega1281? Thanks.

I think the original MEGA had a 1280 so, yes.

The 1281 is in avrdude.conf

#------------------------------------------------------------
# ATmega1281
#------------------------------------------------------------
# Identical to ATmega1280

part
    id               = "m1281";
    desc             = "ATMEGA1281";
    signature        = 0x1e 0x97 0x04;

You’ll need to make a boards.txt entry to reflect this stuff. Will be similar to the 1280 entry that’s there now.
You also lose ports H, J, K, L and UARTs 2 & 3.