Atmega16 SPI to clock out 32bit data
Continuous transactions longer than 8 bits are not possible on ATMega16. You have to poll for SPIF and then load new value. On other MCUs that have double buffered data register, it is possible to reload the data register before it is emptied.

There is no need to assert SS# between words. From SPI's static point of view, in modes 1 or 3, sending 8*4 bits is equivalent to sending 1*32 bits even when it happens seconds apart.