The OPS first post says he has a 904 trans. As such, I don't think he should be worried about no LBA with his valve body. Perhaps a trans expert can confirm but that is typically what is stated as a difference between a 727 and a 904.
I have a CRT 727 in the avatar with a Griner rmvb that has LBA. I start the burnout in the water box in 1st with an almost immediate click to 2nd and then 3rd. Finish the burnout by letting off the throttle and line-loc at the same time allowing the car to move forward at much lower wheel speed and torque. The car could obviously start the burnout in 2nd but I risk the rear tires sliding the car forward with the front tires locked before the rears start spinning. I think this process covers the concern of the sprague breakage as the trans never sees load and immediate slowdown/torque pulse in 1st. Works for me!