140 IR LEDs at 30 MHz using a frequency generator
Seems feasible, but I'd look at a couple of changes / improvements:

Break the array into several chunks and allocate a driver to each chunk
Drive each chunk both low (as you're doing) and high (to discharge the capacitance)
Use SMD LEDs (like 0603's) to reduce capacitance
Use special care in layout to reduce capacitance

LED Risetimes are in the single-ns range, turn-off in the tens of ns. At 30MHz you're at the upper limit of what is possible. More here: What is the latency of an LED?