What spine axles are you using?
I think all the early, pre 35 spline axles Dana 60, had the two piece side gears, I saw the first one piece side gears in a 1970 E body Dana 60.
I have also seen a original 23 spline Dana 60 in a early production (assemble in early Oct of 1969) V code 1970 Charger RT 4 speed car with 4.10 gears shruggy confused
Don't feel bad on this it is not the first time I've seen guys put the wrong axle in the wrong side in a race Dana 60 whiney
Order a rebuild kit from Cass at Dr. Diff to replace those bad clutches and drive plates, make sure the axle engagement is correct also wrench scope

Mr.Cab Racing and winning with Mopars since 1964. (Old F--t, Huh)