I don't have any reason to think there is much, if any, difference from '69-'70. This shows the same data for 1972.
The GCW went down from #10,250 in '69 to #9,500 in '72 for a C20 350 with 4.10 gears.
It isn't going to change a thing for me, what I tow or how I tow.
I'm just interested to see what the 1970 chart says.