Most 69 Z28 trans have "SBC" on the 3 upper tailhousing and 2 shorter tailhousing bolts, and usually "TR" or L5 on the longer singular tailhousing bolt. Either "SBC" or "TR" side cover bolts. Earlier cars pre Jan/69 seem to use the "TR", later cars use "SBC"
I have also seen "RBW" tailhousing bolts.
BTW, lots of trans have mismatched bolts, I dont think the Muncie plant cared, the workers used what ever was in the bin. GM did use different suppliers. FWIW.