I believe Chevy LS motors have a freeze plug style plug in the back pilot hole from the factory. I saw several write-ups about fixing the oil leaks there, while searching for a mystery oil leak on an RB.

1970 Plymouth 'Cuda #'s 440-6(block in storage)currently 493" 6 pack, Shaker, 5 speed Passon, 4.10's
1968 Plymouth Barracuda Convertible 408 Magnum EFI with 4 speed automatic overdrive, 3800 stall lock-up converter and 4.30's (closest thing to an automatic 5 speed going)