I think those bar braces went away on the next generation of trucks. I hadn't seen them until I bought my GMT 400.
On the later trucks the 4L60e has that bellhousing that covers the entire bellhousing (I think they also added more bolts?) and the 4L80e has that bottom cast aluminum cover with the ribs. The sheet metal version went away. Maybe because the LS engine gained an extra bolt on the top of the bellhousing? The 12 o'clock one.
I don't know what the 8.1/4L85e had, but the 8.1/Allison also does not have those braces.