What gear for burnout with 727

Since you have got the GV, why not use it? 2nd-Over is 1.13 ratio. I got rid of that truck shifter that came with my GV in favor of a relay and a Push-ON/Push-OFF microswitch. In fact, I shelved their computer too. It was too slooow shifting. You need to wire an interlock tho to prevent engagement in reverse. That's almost instant destruction to the GV. It only survives that a couple of times and only if you were gentle to it.
Without the computer, shifting is instant.INSTANT.
I use mine as a splitter behind a 4 speed. About 430 to 450 hp.

OK the computer wasn't that much slower...

Another idea might be to convert the line-loc to, push On/push OFF. I guess you'd need an ON-indicator light. I used a 12v LED,under my tach, where the GVOD-ON lite is as well. One is red One is green. But I guess you got lotsa lites already