I suppose you have downloaded AN65974 firmware. Please check the FPGA firmware for Xilinx. You will see there is only one bit-"slavefifo2b_fpga_top.bit" file. The source is also available in the same folder: AN65974\FPGA Source files\fx3_slaveFIFO2b_xilinx\fpga_slavefifo2b_verilog
The various test modes are selected based on the Sw8 pin configuration on the Spartan board. Please see the AN65974 application note Figure 28., and table 6
I'm not sure why I didn't see those files, but thanks for the pointer. They are what I was looking for.