Hi
I don't think it will.
The 6.2 in 84 had a two piece rear seal,and the 6.5 has a one piece rear seal.The end of the crank was changed to accommodate the one piece seal.That change makes the flywheels different for the 1 or 2 piece seal.
90 Chev 3500 c/c 4x4,6.2na,400 auto,4:10 gears.DSG Timing gears,main girdle, isspro tach, pyro,boost,oil and trany temp.Dual Tstats, High volume peninsular pump,on shelf, Custom turbo and intercooler 85%complete. Change of plans for the dually, it's going to get a Cummins. Both trucks are Blue 90 4x4 crews