This definitely works quite well even on a r720xd! But as far as i know a r740 should be able to boot directly without the need of clover

I installed a Tesla P40 in a R720xd. You just have to carefully select the correct cable for power supply.

LED Multiplexing might be worth a look. It reduces the number of GPIOs needed and the code doesn’t get very complicated. You also don’t need any additional chips or special LEDs