I updated this code today. It now fully supports recording 1024 samples. I had accidentally defined the samples as integers and overlooked this fact until this weekend. The timing / padding was redone now that the loops are doing single byte assignments and compared against the OBLS again.
Note that I recently bought a "Seeeduino V2.21 (Atmega 328P)" which has a switch to disable auto-reset. It works really well with this code. Now that I have tried both, I definitely prefer an auto-reset disable switch or jumper over the 120 ohm resistor method.