Double
I had a double rail car door and it was faster after I cut the top rail for more flex. That was with 900 HP with PG.
There are different types of double rails. There are angle bars from the top of the 4 link down to the trans mount to the full rail going all the way to the front motor plate.
Pro Stock cars have them and 1400 HP is enough to consider at least a partial double rail, whether small block or big block, even with PG.