Avalon 8 bit with Nios 32 bit possible?

However, in practise, you don't want to do it.

Instead create a 32bit slave that ignores the high bits on writes and returns zeros on reads.

Remembering to look at the byte enables.

If you have an 8bit slave you'll get a bus width adapter added than generates 4 cycles to your slave for every access done by the nios.

Also, since the nios always asserts all 4 byte enables on reads, the data fifo probably work work properly.